Release sync misses issues linked in PR body when deployed commit message lacks PR or issue metadata

[gsigler]

linear-release-action can miss released work when the Linear issue is linked in the GitHub PR body, but the commit that lands on main does not include either the PR number or the Linear issue key in its commit message.

This causes release sync to omit work that was actually released, even though the PR is correctly linked to the Linear issue and that linkage is already understood by both GitHub and Linear.

Reproduction steps

1. Create a PR targeting main.
2. Link a Linear issue in the PR body using a closing reference such as Fixes ABC-123.
3. Merge the PR so that the resulting commit on main has a plain commit message that does not contain:
   • a PR reference like (#1234)
   • the Linear issue key like ABC-123
4. Run linear-release-action or linear-release sync as part of the deploy workflow.
5. Observe that the release does not include the linked Linear issue.

Expected behavior

• If GitHub can associate the deployed commit with the merged PR, and that PR is linked to a Linear issue in the PR body, release sync should include that issue in the release.

[linear-code]

LIN-72526

[gsigler]

One additional detail that seems important: this appears to happen specifically when the PR is merged by rebasing. In that case, the commit that lands on main can remain a plain commit without the GitHub PR number in the final commit message. By contrast, merge commits that land as Title (#1234) still give release sync a PR reference to detect.

That seems to explain why the behavior is intermittent and depends on merge strategy rather than whether the PR was linked to a Linear issue.