Allow preview release process to comment on PRs

guardian/gha-scala-library-release-workflow#19
introduces support for publishing preview releases, but note this does
use the `pull-requests: write` permission in order to comment on the PR
to announce that the release has been published - so we need to
additionally grant that permission:

https://github.com/guardian/gha-scala-library-release-workflow/pull/19/files#r1441589383

.github/workflows/release.yml

@@ -6,7 +6,7 @@ on:
 jobs:
   release:
     uses: guardian/gha-scala-library-release-workflow/.github/workflows/reusable-release.yml@main
-    permissions: { contents: write }
+    permissions: { contents: write, pull-requests: write }
     secrets:
       SONATYPE_PASSWORD: ${{ secrets.AUTOMATED_MAVEN_RELEASE_SONATYPE_PASSWORD }}
       PGP_PRIVATE_KEY: ${{ secrets.AUTOMATED_MAVEN_RELEASE_PGP_SECRET }}