patch 8.2.3831: opfunc test fails when missing feature changes function name

Problem:    Opfunc test fails when missing feature changes function name.
            (Dominique Pellé)
Solution:   Check the relevant screen line instead of using a screendump.
            (closes #9360)
diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index f97f902..9251266 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -3244,7 +3244,7 @@
 
   var buf = RunVimInTerminal('-S XTest_opfunc_error', {rows: 6, wait_for_ruler: 0})
   WaitForAssert(() => assert_match('Press ENTER', term_getline(buf, 6)))
-  VerifyScreenDump(buf, 'Test_opfunc_error', {})
+  WaitForAssert(() => assert_match('E684: list index out of range: 0', term_getline(buf, 5)))
 
   # clean up
   StopVimInTerminal(buf)