Prevent unintentional Postgres submodule update

[bayandin]

Problem

Postgres submodule can be changed unintentionally, and these changes are easy to miss during the review.
Adding a check that should prevent this from happening, the check fails build-neon job with the following message:

Expected postgres-v14 rev to be at '1414141414141414141414141414141414141414', but it is at '1144aee1661c79eec65e784a8dad8bd450d9df79'
Expected postgres-v15 rev to be at '1515151515151515151515151515151515151515', but it is at '1984832c740a7fa0e468bb720f40c525b652835d'
Please update vendors/revisions.json if these changes are intentional.

This is an alternative approach to #4603

Summary of changes

• Add vendor/revisions.json file with expected revisions
• Add built-time check (to build-neon job) that Postgres submodules match revisions from vendor/revisions.json
• A couple of small improvements for logs from Add Postgres commit sha to Postgres version #4603
• Fixed GitHub autocomment for no tests was run case

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]

1028 tests run: 976 passed, 0 failed, 52 skipped (full report)

---

Flaky tests (2)

Postgres 15

• test_remote_storage_upload_queue_retries[local_fs]: release

Postgres 14

• test_threshold_based_eviction: debug

[koivunej]

Let's test this still with wrong commits but I can't see why it wouldn't work. You beat me to it :) Maybe add just revert 9169c99 so others will see this was tested...?

[bayandin]

Let's test this still with wrong commits but I can't see why it wouldn't work. You beat me to it :) Maybe add just revert 9169c99 so others will see this was tested...?

Here's an example of failed step:

Expected postgres-v14 rev to be at '1414141414141414141414141414141414141414', but it is at '1144aee1661c79eec65e784a8dad8bd450d9df79'
Expected postgres-v15 rev to be at '1515151515151515151515151515151515151515', but it is at '1984832c740a7fa0e468bb720f40c525b652835d'
Please update vendors/revisions.json if these changes are intentional