Skip PR author checklist when melvin-bot[bot] is the author

[rlinoz]

Explanation of Change

The PR Author Checklist workflow (.github/workflows/authorChecklist.yml) runs on every PR opened against main. Its checklist job already skips known bots by comparing github.actor (OSBotify, imgbot[bot]). PRs authored by the Melvin GitHub App run through this job unnecessarily — Melvin is not an external contributor and has no author checklist to fill out.

This adds melvin-bot[bot] to the job-level if skip. melvin-bot[bot] is the github.actor value for the Melvin GitHub App (CONST.NAME_MELVIN_BOT), and matches the existing exclusion precedent in proposalPolice.yml.

Fixed Issues

$ https://expensify.slack.com/archives/C02NK2DQWUX/p1786470305341269?thread_ts=1786111493.247829&cid=C02NK2DQWUX
PROPOSAL:

Tests

This is a CI-only change to a pull_request_target workflow condition; there is no in-app behavior to test.

1. Open a PR authored by melvin-bot[bot] against main and verify the checklist job is skipped.
2. Open a PR authored by a normal user and verify the checklist job still runs.

• Verify that no errors appear in the JS console

Offline tests

N/A — CI workflow change.

QA Steps

// [No QA]

• Verify that no errors appear in the JS console

PR Author Checklist

• I linked the correct issue in the ### Fixed Issues section above
• I wrote clear testing steps that cover the changes made in this PR
• I verified there are no console errors

Screenshots/Videos

N/A — CI workflow change.