Bump rexml in /docs in the doc-gems-security group (#1122)

Bumps the doc-gems-security group with 1 update in the /docs directory: [rexml](https://github.com/ruby/rexml).

Updates `rexml` from 3.4.1 to 3.4.2
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](ruby/rexml@v3.4.1...v3.4.2)

---
updated-dependencies:
- dependency-name: rexml
  dependency-version: 3.4.2
  dependency-type: indirect
  dependency-group: doc-gems-security
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

docs/Gemfile.lock

@@ -248,7 +248,7 @@ GEM
     rb-fsevent (0.11.2)
     rb-inotify (0.11.1)
       ffi (~> 1.0)
-    rexml (3.4.1)
+    rexml (3.4.2)
     rouge (3.30.0)
     rubyzip (2.4.1)
     safe_yaml (1.0.5)