build(deps-dev): 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](ruby/rexml@v3.3.6...v3.3.9)

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

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile.lock

@@ -305,8 +305,7 @@ GEM
       io-console (~> 0.5)
     request_store (1.5.1)
       rack (>= 1.4)
-    rexml (3.3.6)
-      strscan
+    rexml (3.3.9)
     rspec-core (3.13.0)
       rspec-support (~> 3.13.0)
     rspec-expectations (3.13.2)
@@ -388,7 +387,6 @@ GEM
       net-sftp (>= 2.1.2)
       net-ssh (>= 2.8.0)
     stringio (3.1.1)
-    strscan (3.1.0)
     terser (1.2.3)
       execjs (>= 0.3.0, < 3)
     thor (1.3.2)