ci: add workflow to ensure self-contained commits

[snprajwal]

The workflow builds CRIU at each commit in the PR, and fails if any of the commits are not self-contained. This will ensure that we can reliably use git bisect while debugging anything in the repo.

Fixes #2216

[codecov-commenter]

Codecov Report

Patch coverage: 46.66% and project coverage change: -0.04 :warning:

Comparison is base (6cfe7aa) 70.46% compared to head (0b4f474) 70.42%.

:exclamation: Current head 0b4f474 differs from pull request most recent head 3b2e4b6. Consider uploading reports for the commit 3b2e4b6 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## criu-dev #2219 +/- ## ============================================ - Coverage 70.46% 70.42% -0.04% ============================================ Files 133 133 Lines 33596 33545 -51 ============================================ - Hits 23674 23625 -49 + Misses 9922 9920 -2 ``` | [Impacted Files](https://app.codecov.io/gh/checkpoint-restore/criu/pull/2219?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None) | Coverage Δ | | |---|---|---| | [criu/kerndat.c](https://app.codecov.io/gh/checkpoint-restore/criu/pull/2219?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-Y3JpdS9rZXJuZGF0LmM=) | `57.73% <33.33%> (+0.04%)` | :arrow_up: | | [criu/util.c](https://app.codecov.io/gh/checkpoint-restore/criu/pull/2219?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-Y3JpdS91dGlsLmM=) | `64.38% <55.55%> (-0.06%)` | :arrow_down: | ... and [7 files with indirect coverage changes](https://app.codecov.io/gh/checkpoint-restore/criu/pull/2219/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None)

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[Snorch]

Adding some more info on which commit the workflow failed would be nice, see https://github.com/checkpoint-restore/criu/actions/runs/5462129746/jobs/9941059153?pr=2220

[snprajwal]

I hope this works, git rebase is slightly iffy about what can be passed as an exec command (no newlines, apparently).