patch 8.2.3100: Vim9: no error when using type with unknown number of args

Problem:    Vim9: no error when using type with unknown number of arguments.
Solution:   Do not ignore argument count of -1. (closes #8492)
diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index f4142ee..89cdee7 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -1030,7 +1030,7 @@
 
   lines =<< trim END
       vim9script
-      def g:TestFunc(f: func())
+      def g:TestFunc(f: func)
       enddef
       legacy call g:TestFunc({-> 0})
       delfunc g:TestFunc