pr-standards: needs:issue is applied to every v2-targeted PR despite a valid closing reference #51970

Description

pr-standards marks every PR that targets a non-default base with needs:issue, even when the PR description contains Closes #123 / Fixes #123 and the referenced issue exists.

pr-standards.yml reads closingIssuesReferences, which GitHub only populates when a PR targets the repository's default branch (dev). For a v2-targeted PR it is always 0. The v2 copy of the workflow already falls back to matching closing keywords in the description, but pull_request_target runs the workflow from the default branch, so the dev copy is the one that executes and it has no fallback.

Effect: every v2 PR is labelled needs:issue and receives the "This PR doesn't have a linked issue" comment regardless of its description, and editing the description cannot clear it.

Steps to reproduce

1. Open a PR against v2 whose description contains Closes #<open-issue>.
2. Observe needs:issue on the PR and the bot comment, even though the reference is valid.

Expected

A PR that references an existing issue in its description should not be labelled needs:issue for any base branch.

Context

• The fallback exists on v2 only (git diff upstream/dev upstream/v2 -- .github/workflows/pr-standards.yml).
• It does not block merge in practice (fix(tui): don't crash when fs.watch throws (e.g. ENOSPC) #51210 merged with the label), but it is misleading and the comment says the merge is blocked, which wastes contributor and maintainer time.