ci: crnm: rev argument for tags and branches

The --rev argument mentions that it accepts a git revision. I think it would
be practical to describe that it accepts a commit id, as well as a tag or
branch name.

Signed-off-by: Sergi Blanch-Torne <sergi.blanch.torne@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35828>

bin/ci/ci_run_n_monitor.py

@@ -498,7 +498,9 @@ def parse_args() -> argparse.Namespace:
 
     mutex_group1 = parser.add_mutually_exclusive_group()
     mutex_group1.add_argument(
-        "--rev", default="HEAD", metavar="revision", help="repository git revision (default: HEAD)"
+        "--rev",
+        default="HEAD",
+        help="Repository git commit-ish, tag or branch name (default: HEAD)",
     )
     mutex_group1.add_argument(
         "--pipeline-url",