CI: downgrade docker/setup-buildx-action

[bayandin]

Problem

I've bumped docker/setup-buildx-action in #8042 because I wasn't able to reproduce the issue from #7445.
But now the issue appears again in https://github.com/neondatabase/neon/actions/runs/9514373620/job/26226626923?pr=8059
The steps to reproduce aren't clear, it required docker/setup-buildx-action@v3 and rebuilding the image without cache, probably

Summary of changes

• Downgrade docker/setup-buildx-action@v3 to docker/setup-buildx-action@v2

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

[a-masterov]

Looks good

[github-actions]

3216 tests run: 3075 passed, 0 failed, 141 skipped (full report)

---

Flaky tests (1)

Postgres 14

• test_subscriber_restart: release

Code coverage* (full report)

• functions: 31.5% (6633 of 21065 functions)
• lines: 48.6% (51629 of 106286 lines)

* collected from Rust tests only

---

_{The comment gets automatically updated with the latest test results
cb808ba at 2024-06-14T11:51:46.725Z :recycle:}