Bump test-unit from 3.7.1 to 3.7.3

Bumps [test-unit](https://github.com/test-unit/test-unit) from 3.7.1 to 3.7.3.
- [Release notes](https://github.com/test-unit/test-unit/releases)
- [Commits](test-unit/test-unit@3.7.1...3.7.3)

---
updated-dependencies:
- dependency-name: test-unit
  dependency-version: 3.7.3
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Gemfile.lock

@@ -134,7 +134,7 @@ GEM
     rubyzip (3.2.2)
     semver2 (3.4.2)
     stringio (3.2.0)
-    test-unit (3.7.1)
+    test-unit (3.7.3)
       power_assert
     thor (1.4.0)
     thread_safe (0.3.6)