github: sync_labels: match issue number with better pattern
Seen in https://github.com/scylladb/scylladb/actions/runs/8357352616/job/22876314535
```
python .github/scripts/sync_labels.py --repo scylladb/scylladb --number 17309 --action labeled --label backport/none
shell: /usr/bin/bash -e {0}
env:
GITHUB_TOKEN: ***
Found issue number: ('', '', '15465')
Traceback (most recent call last):
File "/home/runner/work/scylladb/scylladb/.github/scripts/sync_labels.py", line 9[3](https://github.com/scylladb/scylladb/actions/runs/8357352616/job/22876314535#step:5:3), in <module>
main()
File "/home/runner/work/scylladb/scylladb/.github/scripts/sync_labels.py", line 89, in main
sync_labels(repo, args.number, args.label, args.action, args.is_issue)
File "/home/runner/work/scylladb/scylladb/.github/scripts/sync_labels.py", line [7](https://github.com/scylladb/scylladb/actions/runs/8357352616/job/22876314535#step:5:8)1, in sync_labels
target = repo.get_issue(int(pr_or_issue_number))
TypeError: int() argument must be a string, a bytes-like object or a real number, not 'tuple'
Error: Process completed with exit code 1.
```
Fixing the pattern to catch all GitHub supported close keywords as
describe in https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword
Fixed: https://github.com/scylladb/scylladb/issues/17917
Fixed: https://github.com/scylladb/scylladb/issues/17921
Closes scylladb/scylladb#17920
5bd6b4f4c2