Add the update-mail-to-commit-notes GitHub Action

The idea is to take over the job of the "Update GitGitGadget's commit to
mail notes" Azure Pipeline over at
https://dev.azure.com/gitgitgadget/git/_build?definitionId=9, making use
of the just-ported logic in `CIHelper`.

This will obviously require a GitHub workflow, too, which is added in
gitgitgadget-workflows/gitgitgadget-workflows#1

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

update-mail-to-commit-notes/action.yml

@@ -0,0 +1,13 @@
+name: 'Update the mail <-> commit notes'
+description: 'Updates the mapping between commits and patch emails, stored in the `mail-to-commit` and `commit-to-mail` Git notes refs.'
+author: 'Johannes Schindelin'
+inputs:
+  pr-repo-token:
+    description: 'The access token to work on the repository that holds PRs and state'
+    required: true
+runs:
+  using: 'node20'
+  main: './index.js'
+branding:
+  icon: 'git-commit'
+  color: 'orange'

update-mail-to-commit-notes/index.js

@@ -0,0 +1,14 @@
+async function run() {
+  const { CIHelper } = await import("../dist/index.js")
+
+  const ci = new CIHelper()
+
+  await ci.setupGitHubAction({
+    needsMailingListMirror: true,
+    needsUpstreamBranches: true,
+    needsMailToCommitNotes: true,
+  })
+  await ci.updateMailToCommitNotes()
+}
+
+run()