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] <support@github.com>

Gemfile.lock

@@ -57,8 +57,7 @@ GEM
     regexp_parser (2.8.3)
     rerun (0.14.0)
       listen (~> 3.0)
-    rexml (3.3.6)
-      strscan
+    rexml (3.3.9)
     rollbar (3.4.2)
     rubocop (1.59.0)
       json (~> 2.3)
@@ -85,7 +84,6 @@ GEM
       rack (~> 2.2, >= 2.2.4)
       rack-protection (= 3.1.0)
       tilt (~> 2.0)
-    strscan (3.1.0)
     tilt (2.3.0)
     unicode-display_width (2.5.0)
     webmock (3.19.1)