patch 8.2.2566: Vim9: Function name is not recognized

Problem:    Vim9: Function name is not recognized.
Solution:   Change lookup_scriptvar() to also find function names.
            (closes #7770)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 77162ec..40e70c3 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -1829,7 +1829,7 @@
 	if (ea.cmd == cmd + 1 && *cmd == '$')
 	    // should be "$VAR = val"
 	    --ea.cmd;
-	p = find_ex_command(&ea, NULL, lookup_scriptvar, NULL);
+	p = find_ex_command(&ea, NULL, lookup_scriptitem, NULL);
 	if (ea.cmdidx == CMD_SIZE)
 	{
 	    char_u *ar = skip_range(ea.cmd, TRUE, NULL);