test_runner: set AWS credentials for endpoints

[bayandin]

Problem

If AWS credentials are not set locally (via AWS_ACCESS_KEY_ID/AWS_SECRET_ACCESS_KEY env vars) test_remote_library[release-pg15-mock_s3] test fails with the following error:

ERROR could not start the compute node: Failed to download a remote file: Failed to download S3 object: failed to construct request

Summary of changes

• set AWS credentials for endpoints programmatically

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

[awestover]

looks good

[awestover]

looks good!

[github-actions]

1264 tests run: 1215 passed, 0 failed, 49 skipped (full report)

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Flaky tests (3)

Postgres 14

• test_partial_evict_tenant: debug
• test_multiple_extensions_one_archive: release
• test_empty_tenant_size: debug