fix showing methods with unicode gensymed variable names (#36396)

(cherry picked from commit 9b2c6b2)

Author: KristofferC

base/methodshow.jl

@@ -13,7 +13,7 @@ function argtype_decl(env, n, sig::DataType, i::Int, nargs, isva::Bool) # -> (ar
     s = string(n)
     i = findfirst(isequal('#'), s)
     if i !== nothing
-        s = s[1:i-1]
+        s = s[1:prevind(s, i)]
     end
     if t === Any && !isempty(s)
         return s, ""

test/show.jl

@@ -1986,3 +1986,12 @@ end
     @test sprint(show, skipmissing([1,2,missing])) == "skipmissing(Union{Missing, $Int}[1, 2, missing])"
     @test sprint(show, skipmissing((missing,1.0,'a'))) == "skipmissing((missing, 1.0, 'a'))"
 end
+
+@testset "unicode in method table" begin
+    αsym = gensym(:α)
+    ℓsym = gensym(:ℓ)
+    eval(:(foo($αsym) = $αsym))
+    eval(:(bar($ℓsym) = $ℓsym))
+    @test contains(string(methods(foo)), "foo(α)")
+    @test contains(string(methods(bar)), "bar(ℓ)")
+end