Update jekyll-seo-tag requirement from 2.8.0 to 2.9.0

Updates the requirements on [jekyll-seo-tag](https://github.com/jekyll/jekyll-seo-tag) to permit the latest version.
- [Release notes](https://github.com/jekyll/jekyll-seo-tag/releases)
- [Changelog](https://github.com/jekyll/jekyll-seo-tag/blob/master/History.markdown)
- [Commits](jekyll/jekyll-seo-tag@v2.8.0...v2.9.0)

---
updated-dependencies:
- dependency-name: jekyll-seo-tag
  dependency-version: 2.9.0
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Gemfile

@@ -4,6 +4,6 @@ gem "jekyll", "4.4.1"
 
 group :jekyll_plugins do
   gem "jekyll-feed", "0.17.0"
-  gem "jekyll-seo-tag", "2.8.0"
+  gem "jekyll-seo-tag", "2.9.0"
   gem "jekyll-sitemap", "1.4.0"
 end