post_version.py: stop adding release candidates to the index and relnotes

Closes: mesa/mesa#2870


Signed-off-by: Eric Engestrom <eric@engestrom.ch>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
Part-of: <mesa/mesa!4929>

bin/post_version.py

@@ -134,12 +134,16 @@ def main() -> None:
     parser.add_argument('version', help="The released version.")
     args = parser.parse_args()
 
-    update_index(args.version)
-    update_release_notes(args.version)
     update_calendar(args.version)
+    done = 'update calendar'
+
+    if not is_release_candidate(args.version):
+        update_index(args.version)
+        update_release_notes(args.version)
+        done += ', add news item, and link releases notes'
+
     subprocess.run(['git', 'commit', '-m',
-                    'docs: update calendar, add news item, and link releases '
-                    f'notes for {args.version}'])
+                    f'docs: {done} for {args.version}'])
 
 
 if __name__ == "__main__":