fix: warn when --tag-filter is used without --list-tags

Assisted-by: OpenCode

Author: zdrapela

skills/prow-trigger-nightly/scripts/trigger_nightly_job.py

@@ -604,6 +604,9 @@ def validate_args(args: argparse.Namespace) -> None:
         log_error("Either --list, --list-tags, or --job is required.")
         sys.exit(1)
 
+    if args.tag_filter and not args.list_tags:
+        log_warn("--tag-filter is only used with --list-tags, ignoring.")
+
     if args.job:
         if not args.job.startswith("periodic-ci-"):
             log_error(f"Job name must start with 'periodic-ci-', got: {args.job}")