patch 8.2.4260: Vim9: can still use a global function without g:

Problem:    Vim9: can still use a global function without g: at the script
            level.
Solution:   Also check for g: at the script level. (issue #9637)
diff --git a/src/testdir/test_ins_complete.vim b/src/testdir/test_ins_complete.vim
index 5cfa462..35cacf2 100644
--- a/src/testdir/test_ins_complete.vim
+++ b/src/testdir/test_ins_complete.vim
@@ -1422,7 +1422,7 @@
     call assert_fails("set completefunc=funcref('abc')", "E700:")
 
     #" set 'completefunc' to a non-existing function
-    set completefunc=CompleteFunc2
+    set completefunc=g:CompleteFunc2
     call setline(1, 'five')
     call assert_fails("set completefunc=function('NonExistingFunc')", 'E700:')
     call assert_fails("LET &completefunc = function('NonExistingFunc')", 'E700:')
@@ -1679,7 +1679,7 @@
     call assert_fails("set omnifunc=funcref('abc')", "E700:")
 
     #" set 'omnifunc' to a non-existing function
-    set omnifunc=OmniFunc2
+    set omnifunc=g:OmniFunc2
     call setline(1, 'nine')
     call assert_fails("set omnifunc=function('NonExistingFunc')", 'E700:')
     call assert_fails("LET &omnifunc = function('NonExistingFunc')", 'E700:')
@@ -1936,7 +1936,7 @@
     call assert_fails("set thesaurusfunc=funcref('abc')", "E700:")
 
     #" set 'thesaurusfunc' to a non-existing function
-    set thesaurusfunc=TsrFunc2
+    set thesaurusfunc=g:TsrFunc2
     call setline(1, 'ten')
     call assert_fails("set thesaurusfunc=function('NonExistingFunc')", 'E700:')
     call assert_fails("LET &thesaurusfunc = function('NonExistingFunc')", 'E700:')