Bump rexml from 3.3.6 to 3.3.9 in /ruby (#7017)

Bumps [rexml](https://github.com/ruby/rexml) from 3.3.6 to 3.3.9.
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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

ruby/Gemfile.lock

@@ -1443,8 +1443,7 @@ GEM
     rainbow (3.1.1)
     rake (13.0.6)
     regexp_parser (2.8.0)
-    rexml (3.3.6)
-      strscan
+    rexml (3.3.9)
     rspec (3.12.0)
       rspec-core (~> 3.12.0)
       rspec-expectations (~> 3.12.0)
@@ -1493,7 +1492,6 @@ GEM
       rack-protection (= 3.0.6)
       tilt (~> 2.0)
     stringio (3.0.7)
-    strscan (3.1.0)
     tilt (2.1.0)
     time (0.2.2)
       date