chore(ci): Fix baseline SHA default for new weekly schedule

[jszwedko]

Summary

#21979 updated the schedule to weekly, but it was still looking for the SHA from 24 hours ago meaning that most commits wouldn't be tested.

Change Type

• Bug fix
• New feature
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

How did you test this PR?

Will be tested by CI.

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the "no-changelog" label to this PR.

Checklist

• Please read our Vector contributor resources.
• If this PR introduces changes Vector dependencies (modifies Cargo.lock), please
  run dd-rust-license-tool write to regenerate the license inventory and commit the changes (if any). More details here.

References

[datadog-vectordotdev]

Datadog Report

Branch report: jszwedko/fix-default-baseline
Commit report: d059d9d
Test service: vector

✅ 0 Failed, 7 Passed, 0 Skipped, 25.46s Total Time