Bump test-unit from 3.6.4 to 3.6.7

Bumps [test-unit](https://github.com/test-unit/test-unit) from 3.6.4 to 3.6.7.
- [Release notes](https://github.com/test-unit/test-unit/releases)
- [Commits](test-unit/test-unit@3.6.4...3.6.7)

---
updated-dependencies:
- dependency-name: test-unit
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile.lock

@@ -132,7 +132,7 @@ GEM
     sass-listen (4.0.0)
       rb-fsevent (~> 0.9, >= 0.9.4)
       rb-inotify (~> 0.9, >= 0.9.7)
-    test-unit (3.6.4)
+    test-unit (3.6.7)
       power_assert
     timers (4.3.5)
     ttfunk (1.8.0)