Bump test-unit from 3.5.5 to 3.5.7

Bumps [test-unit](https://github.com/test-unit/test-unit) from 3.5.5 to 3.5.7.
- [Release notes](https://github.com/test-unit/test-unit/releases)
- [Commits](test-unit/test-unit@3.5.5...3.5.7)

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

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

Author: dependabot[bot]

Gemfile.lock

@@ -7,15 +7,15 @@ GEM
   remote: https://rubygems.org/
   specs:
     docile (1.4.0)
-    power_assert (2.0.1)
+    power_assert (2.0.2)
     rake (13.0.6)
     simplecov (0.21.2)
       docile (~> 1.1)
       simplecov-html (~> 0.11)
       simplecov_json_formatter (~> 0.1)
     simplecov-html (0.12.3)
     simplecov_json_formatter (0.1.4)
-    test-unit (3.5.5)
+    test-unit (3.5.7)
       power_assert
 
 PLATFORMS