ci,cirnm: Fix program name in usage example

Instead of updating the name manually, use the %(prog)s specifier (as
documented at https://docs.python.org/3/library/argparse.html#prog).

Signed-off-by: Matt Coster <matt.coster@imgtec.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/39853>

bin/ci/ci_run_n_monitor.py

@@ -429,7 +429,7 @@ def parse_args() -> argparse.Namespace:
     parser = argparse.ArgumentParser(
         description="Tool to trigger a subset of container jobs "
         + "and monitor the progress of a test job",
-        epilog="Example: mesa-monitor.py --rev $(git rev-parse HEAD) "
+        epilog="Example: %(prog)s --rev $(git rev-parse HEAD) "
         + '--target ".*traces" ',
     )
     parser.add_argument(