Bump rexml from 3.3.6 to 3.3.9

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.6 to 3.3.9.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](https://github.com/ruby/rexml/compare/v3.3.6...v3.3.9)

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

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

Gemfile.lock

@@ -394,8 +394,7 @@ GEM
     responders (3.1.1)
       actionpack (>= 5.2)
       railties (>= 5.2)
-    rexml (3.3.6)
-      strscan
+    rexml (3.3.9)
     rolify (6.0.1)
     rotp (6.3.0)
     rouge (4.1.3)
@@ -517,7 +516,6 @@ GEM
       activesupport (>= 6.1)
       sprockets (>= 3.0.0)
     ssrf_filter (1.1.2)
-    strscan (3.1.0)
     sysexits (1.2.0)
     temple (0.10.3)
     thor (1.3.2)