Bump rexml from 3.3.6 to 3.3.9 (#329)

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

Gemfile.lock

@@ -28,8 +28,7 @@ GEM
       sorbet-runtime (>= 0.5.9204)
     redcarpet (3.6.0)
     regexp_parser (2.9.2)
-    rexml (3.3.6)
-      strscan
+    rexml (3.3.9)
     rspec (3.13.0)
       rspec-core (~> 3.13.0)
       rspec-expectations (~> 3.13.0)
@@ -89,7 +88,6 @@ GEM
       prism (>= 0.28.0)
       sorbet-static-and-runtime (>= 0.5.10187)
       thor (>= 0.19.2)
-    strscan (3.1.0)
     tapioca (0.16.2)
       bundler (>= 2.2.25)
       netrc (>= 0.11.0)