patch 8.2.1375: Vim9: method name with digit not accepted

Problem:    Vim9: method name with digit not accepted.
Solution:   Use eval_isnamec() instead of eval_isnamec1(). (closes #6613)
diff --git a/src/testdir/test_vim9_expr.vim b/src/testdir/test_vim9_expr.vim
index 8be0dea..aa705b2 100644
--- a/src/testdir/test_vim9_expr.vim
+++ b/src/testdir/test_vim9_expr.vim
@@ -1674,14 +1674,14 @@
   return arg
 enddef
 
-def s:EchoArg(arg: any): string
+def s:Echo4Arg(arg: any): string
   return arg
 enddef
 
 def Test_expr7_call()
   assert_equal('yes', 'yes'->Echo())
   assert_equal('yes', 'yes'
-  			->s:EchoArg())
+  			->s:Echo4Arg())
   assert_equal(1, !range(5)->empty())
   assert_equal([0, 1, 2], --3->range())