Bump test-unit from 3.2.7 to 3.2.8

Bumps [test-unit](https://github.com/test-unit/test-unit) from 3.2.7 to 3.2.8.
- [Release notes](https://github.com/test-unit/test-unit/releases)
- [Commits](test-unit/test-unit@3.2.7...3.2.8)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Gemfile.lock

@@ -110,7 +110,7 @@ GEM
     sqlite3 (1.3.13)
     term-ansicolor (1.2.2)
       tins (~> 0.8)
-    test-unit (3.2.7)
+    test-unit (3.2.8)
       power_assert
     thor (0.18.1)
     tins (0.13.2)