Update Rugged to v0.28.4.1

This fixes a number of CVEs in libgit2:
https://github.com/libgit2/rugged/compare/v0.28.3.1..v0.28.4.1

Gemfile.lock

@@ -930,7 +930,7 @@ GEM
     rubyntlm (0.6.2)
     rubypants (0.2.0)
     rubyzip (1.3.0)
-    rugged (0.28.3.1)
+    rugged (0.28.4.1)
     safe_yaml (1.0.4)
     sanitize (4.6.6)
       crass (~> 1.0.2)

changelogs/unreleased/sh-upgrade-rugged.yml

+---
+title: Update Rugged to v0.28.4.1
+merge_request: 21869
+author:
+type: security