[ci/release] Display commit hash in buildkite overview

[krfricke]

Why are these changes needed?

After merging #19803, bisection currentyl displays custom_wheels_url for all runs, which makes it hard to distinguish different commits.

This commit extracts the hash from the custom wheels field to display in buildkite

Example: https://buildkite.com/ray-project/periodic-ci/builds/1614

Related issue number

Checks

• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(