Fix missing `mithril-aggregator` binary in the `stress-test` job

[dlachaume]

Content

This PR includes a fix for the aggregator stress test github workflow. The aggregation node binary required to run the stress test was missing.

Pre-submit checklist

• Branch
  • [ ] Tests are provided (if possible)
  • [ ] Crates versions are updated (if relevant)
  • [ ] CHANGELOG file is updated (if relevant)
  • [x] Commit sequence broadly makes sense
  • [x] Key commits have useful messages
• PR
  • [ ] No clippy warnings in the CI
  • [x] Self-reviewed the diff
  • [x] Useful pull request description
  • [ ] Reviewer requested
• Documentation
  • [ ] Update README file (if relevant)
  • [ ] Update documentation website (if relevant)
  • [ ] Add dev blog post (if relevant)

[github-actions[bot]]

Test Results

    3 files  ±0     43 suites  ±0   8m 27s :stopwatch: +5s   976 tests ±0    976 :white_check_mark: ±0  0 :zzz: ±0  0 :x: ±0  1 070 runs  ±0  1 070 :white_check_mark: ±0  0 :zzz: ±0  0 :x: ±0 

Results for commit 7768fc4d. ± Comparison against base commit b9142036.

:recycle: This comment has been updated with latest results.