build(deps-dev): bump rexml from 3.2.6 to 3.2.8 (#7080)

Bumps [rexml](https://github.com/ruby/rexml) from 3.2.6 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@v3.2.6...v3.2.8)

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

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

Gemfile.lock

@@ -385,7 +385,8 @@ GEM
       redis (>= 3.3)
       resque (>= 1.27)
       rufus-scheduler (~> 3.2, != 3.3)
-    rexml (3.2.6)
+    rexml (3.2.8)
+      strscan (>= 3.0.9)
     rmagick (5.5.0)
       observer (~> 0.1)
       pkg-config (~> 1.4)
@@ -464,6 +465,7 @@ GEM
       activesupport (>= 5.2)
       sprockets (>= 3.0.0)
     stringio (3.1.0)
+    strscan (3.1.0)
     terminal-table (3.0.2)
       unicode-display_width (>= 1.1.1, < 3)
     terser (1.2.2)