patch 8.2.3897: Vim9: second argument of map() and filter() not checked

Problem:    Vim9: the second argument of map() and filter() is not checked at
            compile time.
Solution:   Add more specific type check for the second argument.

src/testdir/test_vim9_script.vim

@@ -2048,7 +2048,7 @@ def Test_vim9script_funcref_other_script()
       return idx % 2 == 1
     enddef
     export def FastFilter(): list<number>
-      return range(10)->filter('FilterFunc')
+      return range(10)->filter('FilterFunc(v:key, v:val)')
     enddef
     export def FastFilterDirect(): list<number>
       return range(10)->filter(FilterFunc)