build: sync between benchies

[koivunej]

Sometimes, the benchmarks fail to start up pageserver in 10s without any obvious reason. Benchmarks run sequentially on otherwise idle runners. Try running sync(2) after each bench to force a cleaner slate.

Implement this via:

• SYNC_AFTER_EACH_TEST environment variable enabled autouse fixture
• autouse fixture seems to be outermost fixture, so it works as expected
• set SYNC_AFTER_EACH_TEST=true for benchmarks in build_and_test workflow

Evidence: https://neon-github-public-dev.s3.amazonaws.com/reports/main/10678984691/index.html#suites/5008d72a1ba3c0d618a030a938fc035c/1210266507534c0f/

[github-actions]

3917 tests run: 3796 passed, 1 failed, 120 skipped (full report)

---

Failures on Postgres 16

• test_basebackup_with_high_slru_count[github-actions-selfhosted-10-13-30]: release-x86-64

# Run all failed tests locally:
scripts/pytest -vv -n $(nproc) -k "test_basebackup_with_high_slru_count[release-pg16-github-actions-selfhosted-10-13-30]"

Flaky tests (6)

Postgres 16

• test_ondemand_wal_download_in_replication_slot_funcs: release-x86-64
• test_scrubber_physical_gc[4]: debug-x86-64
• test_subscriber_restart: release-x86-64, debug-x86-64
• test_tenant_config: debug-x86-64

Postgres 15

• test_location_conf_churn[3]: release-arm64

Code coverage* (full report)

• functions: 32.3% (7430 of 23006 functions)
• lines: 50.5% (60177 of 119170 lines)

* collected from Rust tests only

---

_{The comment gets automatically updated with the latest test results
3072e37 at 2024-09-05T14:23:57.319Z :recycle:}

[koivunej]

Since the first run didn't fail but also didn't sync(1) due to the wrong path, while at the same time a bench run on main again failed with the startup timeout.

I think it would be best to merge this fast as soon as we have evidence of sync being run for a non-zero amount of time and see if it changes anything with the benches on main.

Assuming the current run goes well, could @bayandin add a fix for the comment? Then, let's have a new run and merge.

No failures with the third run either.