Bump test-unit from 3.6.3 to 3.6.4

Bumps [test-unit](https://github.com/test-unit/test-unit) from 3.6.3 to 3.6.4.
- [Release notes](https://github.com/test-unit/test-unit/releases)
- [Commits](test-unit/test-unit@3.6.3...3.6.4)

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

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

Gemfile.lock

@@ -17,7 +17,7 @@ GEM
     simplecov_json_formatter (0.1.4)
     syntax_tree (6.2.0)
       prettier_print (>= 1.2.0)
-    test-unit (3.6.3)
+    test-unit (3.6.4)
       power_assert
 
 PLATFORMS