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)

src/testdir/dumps/Test_opfunc_error.dump

@@ -1,6 +0,0 @@
-|~+0#4040ff13#ffffff0| @73
-|~| @73
-|E+0#ffffff16#e000002|r@1|o|r| |d|e|t|e|c|t|e|d| |w|h|i|l|e| |p|r|o|c|e|s@1|i|n|g| |f|u|n|c|t|i|o|n| |<|S|N|R|>|9|_|O|p|f|u|n|c|:| +0#0000000#ffffff0@19
-|l+0#af5f00255&|i|n|e| @3|2|:| +0#0000000&@64
-|E+0#ffffff16#e000002|6|8|4|:| |l|i|s|t| |i|n|d|e|x| |o|u|t| |o|f| |r|a|n|g|e|:| |0| +0#0000000#ffffff0@42
-|P+0#00e0003&|r|e|s@1| |E|N|T|E|R| |o|r| |t|y|p|e| |c|o|m@1|a|n|d| |t|o| |c|o|n|t|i|n|u|e> +0#0000000&@35

src/testdir/test_vim9_func.vim

@@ -3244,7 +3244,7 @@ def Run_Test_opfunc_error()
 
   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)

src/version.c

@@ -749,6 +749,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3831,
 /**/
     3830,
 /**/