CI flake: Smoketests (Linux)

[clockwork-labs-bot]

Detected by CI Gremlin after a failed merge-queue run succeeded in a later merge-queue run without a new PR head commit.

Tests:

• Smoketests (Linux)

Error:
fatal: couldn't find remote ref refs/heads/gh-readonly-queue/master/pr-5474-16aadbf0bf2a5e3d262407eb1e5e0cab6e4fc998
The process '/usr/bin/git' failed with exit code 128

Failed job runs:

• https://github.com/clockworklabs/SpacetimeDB/actions/runs/28712822986/job/85149298819 (Smoketests (Linux), attempt merge queue run 28712822986 -> merge queue run 28713805519)

Context:

• Merge queue PR: Fix CLI build.rs rebuild triggers #5474
• PR head SHA: 16aadbf
• Later successful run: https://github.com/clockworklabs/SpacetimeDB/actions/runs/28713805519

[clockwork-labs-bot]

Diagnosis for the linked job/attempt only:

• Job: Smoketests (Linux), run 28712822986, job 85149298819, attempt 1.
• The job failed in Checkout sources; no smoketests ran.
• Find Git ref set GIT_REF=refs/heads/gh-readonly-queue/master/pr-5474-16aadbf0bf2a5e3d262407eb1e5e0cab6e4fc998 because PR_NUMBER was empty for the merge queue run.
• actions/checkout@v4 tried to fetch that exact ref three times and GitHub returned fatal: couldn't find remote ref ... each time. The job ended with git exit code 128.
• Root cause visible from this attempt: checkout was given a merge-queue branch ref that was not present on the remote by the time the job fetched it. This is merge-queue/ref lifetime infrastructure failure, not a Linux smoketest failure. The Node 20 deprecation warning is noise in this attempt.

Suggested updated title:
CI flake: Smoketests (Linux) checkout failed on missing merge queue ref

Potential duplicates in the Test flakes project:

• CI flake: Test Suite #5482, CI flake: Index Scan Bench #5484, CI flake: Keynote Bench #5485 are the same run, same merge queue ref, same checkout failure, split across sibling jobs.
• CI flake: couldn't find remote ref #5308 is the same failure mode on another merge queue ref in Smoketests (Windows).
• CI flake: Smoketests (Windows) - couldn't find remote ref #5368 is the same failure mode on another merge queue ref in Smoketests (Windows), but it is closed.

Top duplicate candidate: #5482, because it is the same run/ref/attempt failure and is the first sibling ticket for this incident. If choosing a broader canonical infrastructure ticket instead of sibling tickets, #5308 is the closest existing open prior ticket, but it is a different merge queue ref and job.