Release checklist: small tweaks

Adding a few extra reminders to the release checklist based on today's release.

Author: jrfnl

.github/release-checklist.md

@@ -2,10 +2,13 @@
 
 1. change version in `src/Application.php`
 2. change version and date in `CHANGELOG.md`
-3. add new Git tag
-4. create [new release on GitHub](https://github.com/php-parallel-lint/PHP-Parallel-Lint/releases) with summary of important changes with respect to last version
-5. to Github release add diff link, e.g.
-
-```
-For the details you can have a look at the [diff](https://github.com/php-parallel-lint/PHP-Parallel-Lint/compare/v1.0.0...v1.1.0).
-```
+3. open a new milestone for the next release
+4. move any issues/PRs which were milestoned for the current release, but didn't make it to the next milestone
+5. close the milestone for this release
+6. add new Git tag and push it
+7. edit the [draft release on GitHub](https://github.com/php-parallel-lint/PHP-Parallel-Lint/releases) (which is automatically created by the workflow) with summary of important changes with respect to last version
+8. to Github release add diff link, e.g.
+    ```
+    For the details you can have a look at the [diff](https://github.com/php-parallel-lint/PHP-Parallel-Lint/compare/v1.0.0...v1.1.0).
+    ```
+9. make public notification about the release on Twitter (X) and Mastodon