Bump rexml from 3.2.5 to 3.2.8 in /test/using_bundler (#107)

Bumps [rexml](https://github.com/ruby/rexml) from 3.2.5 to 3.2.8.
- [Release notes](https://github.com/ruby/rexml/releases)
- [Changelog](https://github.com/ruby/rexml/blob/master/NEWS.md)
- [Commits](ruby/rexml@v3.2.5...v3.2.8)

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

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

test/using_bundler/Gemfile.lock

@@ -7,7 +7,8 @@ GEM
       ast (~> 2.4.1)
     rainbow (3.0.0)
     regexp_parser (2.1.1)
-    rexml (3.2.5)
+    rexml (3.2.8)
+      strscan (>= 3.0.9)
     rubocop (1.18.1)
       parallel (~> 1.10)
       parser (>= 3.0.0.0)
@@ -20,6 +21,7 @@ GEM
     rubocop-ast (1.9.0)
       parser (>= 3.0.1.1)
     ruby-progressbar (1.11.0)
+    strscan (3.1.0)
     unicode-display_width (2.0.0)
 
 PLATFORMS