build(deps-dev): bump rexml from 3.3.2 to 3.3.9

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.2 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@v3.3.2...v3.3.9)

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

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

Gemfile.lock

@@ -63,8 +63,7 @@ GEM
       rack (>= 3)
       webrick (~> 1.8)
     regexp_parser (2.9.2)
-    rexml (3.3.2)
-      strscan
+    rexml (3.3.9)
     rspec (3.13.0)
       rspec-core (~> 3.13.0)
       rspec-expectations (~> 3.13.0)
@@ -83,7 +82,6 @@ GEM
       rexml (~> 3.2, >= 3.2.5)
       rubyzip (>= 1.2.2, < 3.0)
       websocket (~> 1.0)
-    strscan (3.1.0)
     thread_safe (0.3.6)
     virtus (2.0.0)
       axiom-types (~> 0.1)