chore: prepare v1.27.3 release and guard template publishing

.github/release-notes/v1.27.3.md

@@ -0,0 +1,22 @@
+FEATURES
+
+- RELEASE
+    - Include English and Simplified Chinese README and CONTRIBUTING files in the release archives
+    - Use reviewed release notes in the publishing workflow
+
+BUGFIXES
+
+- THEMES (Bloom, Ember, Heritage)
+    - Fix pull request push notification commit links and abbreviated hashes for Gitea 1.27.1–1.27.3 by reading `.UserCommit.GitCommit.ID`
+- CI
+    - Add a push notification regression test covering all 10 themes and run Go tests before packaging a release
+
+DOCS
+
+- Verify compatibility with Gitea 1.27.3; its mail templates, mailer, and locale files are unchanged from 1.27.2
+- Correct the compatibility matrix to distinguish the affected v1.27.2 archive from this fixed release
+
+
+---
+
+**Full Changelog:** [v1.27.2...v1.27.3](https://github.com/KenanZhu/GiteaMailTemplates/compare/v1.27.2...v1.27.3)