CI(test-images): add dockerhub auth

[bayandin]

Problem

Unable to find image 'neondatabase/neon:9583413584' locally
docker: Error response from daemon: toomanyrequests: You have reached your pull rate limit. You may increase the limit by authenticating and upgrading: https://www.docker.com/increase-rate-limit.

https://github.com/neondatabase/neon/actions/runs/9583413584/job/26427236409?pr=8112

Summary of changes

• add docker/login-action@v3 for test-images job

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

3228 tests run: 3111 passed, 0 failed, 117 skipped (full report)

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Code coverage* (full report)

• functions: 32.3% (6843 of 21165 functions)
• lines: 49.7% (53395 of 107360 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
ec3669e at 2024-06-19T16:53:28.841Z :recycle:}