Bump autoprefixer-rails from 10.4.19.0 to 10.4.21.0

Bumps [autoprefixer-rails](https://github.com/ai/autoprefixer-rails) from 10.4.19.0 to 10.4.21.0.
- [Changelog](https://github.com/ai/autoprefixer-rails/blob/master/CHANGELOG.md)
- [Commits](ai/autoprefixer-rails@10.4.19.0...10.4.21.0)

---
updated-dependencies:
- dependency-name: autoprefixer-rails
  dependency-version: 10.4.21.0
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

Gemfile.lock

@@ -16,7 +16,7 @@ GEM
       console (~> 1.29)
       fiber-annotation
       io-event (~> 1.6, >= 1.6.5)
-    autoprefixer-rails (10.4.19.0)
+    autoprefixer-rails (10.4.21.0)
       execjs (~> 2)
     bigdecimal (3.1.8)
     colorator (1.1.0)
@@ -89,6 +89,10 @@ GEM
       jekyll (>= 3.3, < 5.0)
     jekyll-sass-converter (3.0.0)
       sass-embedded (~> 1.54)
+    jekyll-seo-tag (2.8.0)
+      jekyll (>= 3.8, < 5.0)
+    jekyll-sitemap (1.4.0)
+      jekyll (>= 3.7, < 5.0)
     jekyll-watch (2.2.1)
       listen (~> 3.0)
     json (2.9.0)
@@ -161,6 +165,8 @@ DEPENDENCIES
   jekyll-paginate-v2 (= 3.0.0)
   jekyll-redirect-from
   jekyll-sass-converter (~> 3.0)
+  jekyll-seo-tag
+  jekyll-sitemap
   tzinfo-data
   webrick (~> 1.8)