patch 8.2.4324: Vim9: script-local function name can start with "_"

Problem:    Vim9: script-local function name can start with "_".
Solution:   Check for leading capital after "s:".  Correct error message.
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 080a53c..debead4 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -888,7 +888,7 @@
 	return NULL;
     if (!ASCII_ISUPPER(is_global ? name_start[2] : name_start[0]))
     {
-	semsg(_(e_function_name_must_start_with_capital_or_s_str), name_start);
+	semsg(_(e_function_name_must_start_with_capital_str), name_start);
 	return NULL;
     }