minor code quality improvements (#39159)

Author: aviatesk

base/accumulate.jl

@@ -441,7 +441,7 @@ function _accumulate1!(op, B, v1, A::AbstractVector, dim::Integer)
     inds = LinearIndices(A)
     inds == LinearIndices(B) || throw(DimensionMismatch("LinearIndices of A and B don't match"))
     dim > 1 && return copyto!(B, A)
-    (i1, state) = iterate(inds) # We checked earlier that A isn't empty
+    (i1, state) = iterate(inds)::NTuple{2,Any} # We checked earlier that A isn't empty
     cur_val = v1
     B[i1] = cur_val
     next = iterate(inds, state)

base/toml_parser.jl

@@ -658,9 +658,12 @@ end
 
 function push!!(v::Vector, el)
     T = eltype(v)
-    if el isa T || typeof(el) === T
+    t = typeof(el)
+    if el isa T || t === T
         push!(v, el::T)
         return v
+    elseif T === Union{}
+        return t[el]
     else
         if typeof(T) === Union
             newT = Any