patch 8.2.1183: assert_fails() checks the last error message

Problem:    assert_fails() checks the last error message.
Solution:   Check the first error, it is more relevant.  Fix all the tests
            that rely on the old behavior.
diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index 77ada94..5ea2945 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -746,7 +746,7 @@
 def Test_unknown_function()
   CheckDefExecFailure([
       'let Ref: func = function("NotExist")',
-      'delfunc g:NotExist'], 'E130:')
+      'delfunc g:NotExist'], 'E700:')
 enddef
 
 def RefFunc(Ref: func(string): string): string