Bump test-unit from 3.5.7 to 3.5.9

Bumps [test-unit](https://github.com/test-unit/test-unit) from 3.5.7 to 3.5.9.
- [Release notes](https://github.com/test-unit/test-unit/releases)
- [Commits](test-unit/test-unit@3.5.7...3.5.9)

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

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

Gemfile.lock

@@ -261,7 +261,7 @@ GEM
       temple (~> 0.10.0)
       tilt (>= 2.0.6, < 2.2)
     temple (0.10.0)
-    test-unit (3.5.7)
+    test-unit (3.5.9)
       power_assert
     tilt (2.1.0)
     time (0.2.1)