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

@@ -15,8 +15,7 @@ GEM
     racc (1.8.0)
     rainbow (3.1.1)
     regexp_parser (2.9.2)
-    rexml (3.3.6)
-      strscan
+    rexml (3.3.9)
     rubocop (1.51.0)
       json (~> 2.3)
       parallel (~> 1.10)
@@ -32,7 +31,6 @@ GEM
     ruby-debian (0.3.8)
     ruby-progressbar (1.13.0)
     ruby-xz (1.0.3)
-    strscan (3.1.0)
     test-unit (3.6.2)
       power_assert
     unicode-display_width (2.5.0)