fix(ci): support hotfix branches in backcompat workflow

[Alenar]

Content

This PR includes a fix to the backward compatibility github actions workflow in order to make it support hotfix branches.

Without this fix the summary job of the workflow fails with the following error:

jq: error (at ./test-results/summary.json:83): Invalid numeric literal at EOF at line 1, column 13 (while parsing '2543.1-hotfix')

Pre-submit checklist

• Branch
  • Commit sequence broadly makes sense
  • Key commits have useful messages
• PR
  • All check jobs of the CI have succeeded
  • Self-reviewed the diff
  • Useful pull request description
  • Reviewer requested
• Documentation
  • No new TODOs introduced

[github-actions]

Test Results

    4 files  ±0    168 suites  ±0   23m 46s ⏱️ -3s
2 210 tests ±0  2 210 ✅ ±0  0 💤 ±0  0 ❌ ±0 
6 895 runs  ±0  6 895 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 1d0d30a. ± Comparison against base commit 2c3dd53.

[jpraynaud]

LGTM