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_menu.vim b/src/testdir/test_menu.vim
index 4fd2828..38098a1 100644
--- a/src/testdir/test_menu.vim
+++ b/src/testdir/test_menu.vim
@@ -153,7 +153,7 @@
   call assert_fails('menu Test.Foo.Bar', 'E327:')
   call assert_fails('cmenu Test.Foo', 'E328:')
   call assert_fails('emenu x Test.Foo', 'E475:')
-  call assert_fails('emenu Test.Foo.Bar', 'E334:')
+  call assert_fails('emenu Test.Foo.Bar', 'E327:')
   call assert_fails('menutranslate Test', 'E474:')
 
   silent! unmenu Foo