bin/gen_release_notes.py: strip '#' from gitlab bugs

If they use the `Fixes: #1` form.

Fixes: 86079447da
       ("scripts: Add a gen_release_notes.py script")
Reviewed-by: Eric Engestrom <eric@engestrom.ch>
Reviewed-by: Juan A. Suarez <jasuarez@igalia.com>
(cherry picked from commit df3d4ad82d)

bin/gen_release_notes.py

@@ -149,7 +149,7 @@ async def gather_bugs(version: str) -> typing.List[str]:
             # This means we have a bug in the form "Closes: https://..."
             issues.append(os.path.basename(urllib.parse.urlparse(bug).path))
         else:
-            issues.append(bug)
+            issues.append(bug.lstrip('#'))
 
     loop = asyncio.get_event_loop()
     async with aiohttp.ClientSession(loop=loop) as session: