Bump test-unit from 3.3.7 to 3.3.8

Bumps [test-unit](https://github.com/test-unit/test-unit) from 3.3.7 to 3.3.8.
- [Release notes](https://github.com/test-unit/test-unit/releases)
- [Commits](test-unit/test-unit@3.3.7...3.3.8)

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

Gemfile.lock

@@ -98,7 +98,7 @@ GEM
     sync (0.5.0)
     term-ansicolor (1.7.1)
       tins (~> 1.0)
-    test-unit (3.3.7)
+    test-unit (3.3.8)
       power_assert
     thor (1.0.1)
     tins (1.26.0)