Bump rexml from 3.3.4 to 3.3.9

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.4 to 3.3.9.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](ruby/rexml@v3.3.4...v3.3.9)

---
updated-dependencies:
- dependency-name: rexml
  dependency-type: indirect
...

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

Author: dependabot[bot]

Gemfile.lock

@@ -293,8 +293,7 @@ GEM
     responders (3.1.1)
       actionpack (>= 5.2)
       railties (>= 5.2)
-    rexml (3.3.4)
-      strscan
+    rexml (3.3.9)
     rouge (4.3.0)
     rspec-core (3.13.0)
       rspec-support (~> 3.13.0)
@@ -380,7 +379,6 @@ GEM
       actionpack (>= 6.1)
       activesupport (>= 6.1)
       sprockets (>= 3.0.0)
-    strscan (3.1.0)
     thor (1.3.1)
     thread_safe (0.3.6)
     tilt (2.4.0)