fix(ci): skip PR lookup on master pushes

[frahlg]

Accepted text proposal

Issue or Discussion: Maintainer task on 2026-08-16.

Maintainer comment that accepted this scope: Fix the repeated master failure from gh pr view "" once and for all.

What changed

The contract-pair step now calls gh pr view only for pull_request events. A push to master compares against srcfl/ftw-webapp@main without trying to find a pull request.

Why

Master test run 31936509902 failed before any product suite ran:

gh pr view ""
no pull requests found for branch "master"

The workflow used github.event.pull_request.number on both pull-request and push events. That field is empty on a push.

Boundaries and safety

This changes one CI workflow step. It does not change runtime code, release workflows, contract files, or the paired app. Pull requests still read the live PR body so a declared Contract-pair branch keeps working.

Open PRs touching this file were checked: #735, #736, #785, and #876. This PR only fixes the event handling that those branches will inherit when rebased.

Verification

• Parsed .github/workflows/test.yml with Ruby YAML.
• Ran actionlint v1.7.7 on the workflow.
• Ran the exact workflow step with EVENT_NAME=push: it selected srcfl/ftw-webapp@main without a PR lookup.
• Ran the exact workflow step with EVENT_NAME=pull_request and PR chore(ci): bump actions/setup-python from 6 to 7 #785: it read the PR and selected srcfl/ftw-webapp@main.
• Ran git diff --check.

Checklist

• The diff implements one accepted scope and does not add follow-on work.
• I checked open pull requests that touch the same files.
• Tests cover the changed behaviour and its failure path.
• A human reviewed every changed web/UI view in a browser, or no UI changed.
• A Changeset is included, or the change is exempt.
• Every commit has a DCO sign-off.