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:development
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

Gemfile.lock

@@ -144,7 +144,7 @@ GEM
     strscan (3.1.0)
     terminal-table (3.0.2)
       unicode-display_width (>= 1.1.1, < 3)
-    test-unit (3.6.3)
+    test-unit (3.6.4)
       power_assert
     tzinfo (2.0.6)
       concurrent-ruby (~> 1.0)