build(deps): update mkdocs-rss-plugin requirement

Updates the requirements on [mkdocs-rss-plugin](https://github.com/Guts/mkdocs-rss-plugin) to permit the latest version.
- [Release notes](https://github.com/Guts/mkdocs-rss-plugin/releases)
- [Changelog](https://github.com/Guts/mkdocs-rss-plugin/blob/main/CHANGELOG.md)
- [Commits](Guts/mkdocs-rss-plugin@1.14.0...1.16.0)

---
updated-dependencies:
- dependency-name: mkdocs-rss-plugin
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

requirements.txt

@@ -9,4 +9,4 @@ pre-commit>=3.8,<4
 # -----------------------
 
 mkdocs-glightbox>=0.3,<0.5
-mkdocs-rss-plugin>=1.14,<1.16
+mkdocs-rss-plugin>=1.14,<1.17