minor fixup for #55705 (#55726)

Author: aviatesk

base/compiler/abstractinterpretation.jl

@@ -2232,7 +2232,8 @@ function abstract_throw_methoderror(interp::AbstractInterpreter, argtypes::Vecto
     elseif !isvarargtype(argtypes[2])
         MethodError
     else
-        tmerge(𝕃ᵢ, MethodError, ArgumentError)
+        ⊔ = join(typeinf_lattice(interp))
+        MethodError ⊔ ArgumentError
     end
     return CallMeta(Union{}, exct, EFFECTS_THROWS, NoCallInfo())
 end

test/compiler/inference.jl

@@ -6137,3 +6137,7 @@ end == TypeError
 @test Base.infer_exception_type((Char,)) do x
     invoke(f_invoke_exct, Tuple{Number}, x)
 end == TypeError
+
+@test Base.infer_exception_type((Vector{Any},)) do args
+    Core.throw_methoderror(args...)
+end == Union{MethodError,ArgumentError}