Migrate tests to GitHub Actions

[eloquence]

Migrates make test and make reprotest tests to GitHub Actions and removes the CircleCI configuration.

Fixes #482.

Test plan

• Visual review of configuration
• Inspect test results to ensure same tests are running as previously

[eloquence]

This is ready for review, but does not include make reprotest yet -- the test is runnable, but it failed on https://github.com/freedomofpress/securedrop-builder/actions/runs/8745779791/job/24001431722. I'd like to determine if that's an expected failure or if it's not running correctly for some reason. (And yeah, then we can add a nightly as well.)

On the other hand, the CircleCI config appears to be borked on this repo -- CircleCI is complaining about lack of SSH checkout key. I defer to the SD team if that's worth fixing before we've got the job switched over. If not, I can poke more at it Monday/Tuesday to finish things up.

[eloquence]

Re: reprotest, I do see a lot of warning: Not a git repository. Use --no-index to compare two paths outside a working tree, so it does not look like an expected test failure but potentially a need to adapt the checkout logic in that test flow.

[eloquence]

reprotest is passing now. 🎉 The issue was twofold:

• We need to set git's safe.directory option for the git operations to succeed
• As per CircleCI config, we need to avoid running tests as root due to tar reproducibility issues when run as root

This PR is also removing the CircleCI config, so CircleCI is complaining now, but if the rest of it looks good, we can remove the CircleCI config fully from this repo prior to merge.

[eloquence]

This in-place patching goes back to 18770bd and, if it was still relevant at all, was not necessary for the wheel reproducibility checks, which do not use the reprotest package that is being patched here. The actual Debian reproducibility check has been migrated into securedrop-client and no longer uses reprotest.

[legoktm]

Awesome, LGTM! We will want to move these jobs to bookworm ASAP now (c.f. freedomofpress/securedrop-client#1958) but we can do that in a separate PR. Will poke infra for the CircleCI disconnect.