fix(ci): apply the PR body issue fallback on the default branch copy - #51058

Issue for this PR

Fixes #51057 (#51057)

Type of change

• Bug fix

What does this PR do?

#43964 taught pr-standards to fall back to the PR description, because closingIssuesReferences is
only populated when a PR targets the default branch. That change landed on v2 and never reached dev,
and pull_request_target runs the default branch's copy of the workflow — so the fallback exists in the
tree that ships and is dead in the copy that executes. The job log of #51052 is the proof: its
check-standards script contains if (linkedIssues === 0) and no hasBodyIssueRef.

This copies those same nine lines into dev's file. No other behavior changes; PRs against dev are
unaffected in practice because they already get a real closing reference.

Disclosure: two of the mislabeled PRs are mine (#51038, #51052), so merging this removes a label from my
own work. #51035 and #51043 are other people's and carry the same label for the same reason.

How did you verify your code works?

• Parsed both files with PyYAML, extracted the check-standards github-script body from each, and compared: after this change the dev copy's script is identical to the v2 copy's.
• Extracted script passes node --check, so the insertion cannot break the embedded JS, and it sits inside the existing script: | block at the same indentation, so the YAML structure is unchanged (both jobs still parse).
• Replayed the two fallback regexes in Node against the live descriptions of fix(cli): pick a Windows bash for the curl installer #51038, fix(server): resolve the configured shell for session terminals #51052, fix(session-ui): fall back when copying code blocks on insecure origins #51035 and fix(tui): show expanded exploration state #51043, pairing each with the closingIssuesReferences.totalCount the API returns for it today (all four are 0): all four evaluate as "issue referenced", i.e. needs:issue would be removed instead of added.
• Observed directly after opening this PR: fix(ci): apply the PR body issue fallback on the default branch copy #51058 (base dev) reports closingIssuesReferences = [51057] and carries no label, while fix(server): resolve the configured shell for session terminals #51052 (base v2, same author, same template) reports 0 and was labeled. Same account, same hour, only the base branch differs.
• Not verified: I have no Bun here, and a workflow cannot be exercised without a real event, so the end-to-end run on dev after merge is still the missing confirmation.

Screenshots / recordings

No UI change.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

"Tested locally" is the file/script comparison, the syntax check and the regex replay above; the workflow itself was not executed.