Fix error hint for missing(1) (#58250)

Before:

```julia-repl
julia> missing(1)
ERROR: MethodError: objects of type Missing are not callable.
In case you did not try calling it explicitly, check if a Missing has been passed as an argument to a method that expects a callable instead.
The object of type `Missing` exists, but no method is defined for this combination of argument types when trying to treat it as a callable object.┌ Error: Hint-handler nonsetable_type_hint_handler for MethodError in Base caused an error
│   exception =
│    1-element ExceptionStack:
│    TypeError: non-boolean (Missing) used in boolean context
│    Stacktrace:
│      [1] nonsetable_type_hint_handler(io::Any, ex::Any, arg_types::Any, kwargs::Any)
│        @ Base ./errorshow.jl:1054
│      [2] show_error_hints(::IOContext{Base.TTY}, ::MethodError, ::Vector{Any}, ::Vararg{Vector{Any}})
│        @ Base.Experimental ./experimental.jl:322
│      [3] showerror(io::IO, ex::MethodError)
│        @ Base ./errorshow.jl:374
│      [4] showerror(io::IOContext{Base.TTY}, ex::MethodError, bt::Vector{Base.StackTraces.StackFrame}; backtrace::Bool)
│        @ Base ./errorshow.jl:106
│      [5] show_exception_stack(io::IOContext{Base.TTY}, stack::Base.ExceptionStack)
│        @ Base ./errorshow.jl:1017
│      [6] display_error(io::IOContext{Base.TTY}, stack::Base.ExceptionStack)
│        @ Base ./client.jl:117
│      [7] repl_display_error(errio::IO, errval::Any)
│        @ REPL ~/.julia/juliaup/julia-nightly/share/julia/stdlib/v1.13/REPL/src/REPL.jl:565
│      [8] print_response(errio::IO, response::Any, backend::Union{Nothing, REPL.REPLBackendRef}, show_value::Bool, have_color::Bool, specialdisplay::Union{Nothing, AbstractDisplay})
│        @ REPL ~/.julia/juliaup/julia-nightly/share/julia/stdlib/v1.13/REPL/src/REPL.jl:582
│      [9] (::REPL.var"#print_response##0#print_response##1"{REPL.LineEditREPL, Pair{Any, Bool}, Bool, Bool})(io::Any)
│        @ REPL ~/.julia/juliaup/julia-nightly/share/julia/stdlib/v1.13/REPL/src/REPL.jl:556
│     [10] with_repl_linfo(f::Any, repl::REPL.LineEditREPL)
│        @ REPL ~/.julia/juliaup/julia-nightly/share/julia/stdlib/v1.13/REPL/src/REPL.jl:829
│     [11] print_response(repl::REPL.AbstractREPL, response::Any, show_value::Bool, have_color::Bool)
│        @ REPL ~/.julia/juliaup/julia-nightly/share/julia/stdlib/v1.13/REPL/src/REPL.jl:554
│     [12] (::REPL.var"#do_respond#73"{Bool, Bool, REPL.var"#setup_interface##12#setup_interface##13"{REPL.LineEditREPL, REPL.REPLHistoryProvider}, REPL.LineEditREPL, REPL.LineEdit.Prompt})(s::REPL.LineEdit.MIState, buf::Any, ok::Bool)
│        @ REPL ~/.julia/juliaup/julia-nightly/share/julia/stdlib/v1.13/REPL/src/REPL.jl:1186
│     [13] run_interface(terminal::REPL.Terminals.TextTerminal, m::REPL.LineEdit.ModalInterface, s::REPL.LineEdit.MIState)
│        @ REPL.LineEdit ~/.julia/juliaup/julia-nightly/share/julia/stdlib/v1.13/REPL/src/LineEdit.jl:2852
│     [14] run_frontend(repl::REPL.LineEditREPL, backend::REPL.REPLBackendRef)
│        @ REPL ~/.julia/juliaup/julia-nightly/share/julia/stdlib/v1.13/REPL/src/REPL.jl:1657
│     [15] (::REPL.var"#61#62"{REPL.LineEditREPL, REPL.REPLBackendRef})()
│        @ REPL ~/.julia/juliaup/julia-nightly/share/julia/stdlib/v1.13/REPL/src/REPL.jl:648
└ @ Base.Experimental experimental.jl:325

Stacktrace:
 [1] top-level scope
   @ REPL[1]:1
```

After:

```julia-repl
julia> missing(1)
ERROR: MethodError: objects of type Missing are not callable.
In case you did not try calling it explicitly, check if a Missing has been passed as an argument to a method that expects a callable instead.
The object of type `Missing` exists, but no method is defined for this combination of argument types when trying to treat it as a callable object.
Stacktrace:
 [1] top-level scope
   @ REPL[3]:1
```

---------

Co-authored-by: Ian Butterworth <i.r.butterworth@gmail.com>

Author: mbauman

base/errorshow.jl

@@ -1056,7 +1056,7 @@ Experimental.register_error_hint(noncallable_number_hint_handler, MethodError)
 #    eg: d = Dict; d["key"] = 2
 function nonsetable_type_hint_handler(io, ex, arg_types, kwargs)
     @nospecialize
-    if ex.f == setindex!
+    if ex.f === setindex!
         T = arg_types[1]
         if T <: Number
             print(io, "\nAre you trying to index into an array? For multi-dimensional arrays, separate the indices with commas: ")

test/errorshow.jl

@@ -406,6 +406,8 @@ let err_str,
     @test occursin("MethodError: no method matching Bool()", err_str)
     err_str = @except_str :a() MethodError
     @test occursin("MethodError: objects of type Symbol are not callable", err_str)
+    err_str = @except_str missing(1) MethodError
+    @test occursin("MethodError: objects of type Missing are not callable", err_str)
     err_str = @except_str EightBitType() MethodError
     @test occursin("MethodError: no method matching $(curmod_prefix)EightBitType()", err_str)
     err_str = @except_str i() MethodError