Bump test-unit from 3.5.5 to 3.5.7 (#2657)

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](https://github.com/test-unit/test-unit/compare/3.5.5...3.5.7)

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

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Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Gemfile.lock

@@ -198,7 +198,7 @@ GEM
     sync (0.5.0)
     term-ansicolor (1.7.1)
       tins (~> 1.0)
-    test-unit (3.5.5)
+    test-unit (3.5.7)
       power_assert
     test-unit-context (0.5.1)
       test-unit (>= 2.4.0)