Bump test-unit from 3.7.1 to 3.7.7 (#3172)

Bumps [test-unit](https://github.com/test-unit/test-unit) from 3.7.1 to 3.7.7.
- [Release notes](https://github.com/test-unit/test-unit/releases)
- [Commits](test-unit/test-unit@3.7.1...3.7.7)

---
updated-dependencies:
- dependency-name: test-unit
  dependency-version: 3.7.7
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

Gemfile

@@ -15,6 +15,6 @@ gem 'rubocop', '1.81.7'
 gem 'rubocop-minitest', '0.38.2'
 gem 'rubocop-rake', '0.7.1'
 gem 'simplecov', '0.22.0'
-gem 'test-unit', '3.7.1'
+gem 'test-unit', '3.7.7'
 gem 'timecop', '0.9.10'
 gem 'yard', '0.9.38'

Gemfile.lock

@@ -81,7 +81,7 @@ GEM
     simplecov-html (0.13.2)
     simplecov_json_formatter (0.1.4)
     stringio (3.2.0)
-    test-unit (3.7.1)
+    test-unit (3.7.7)
       power_assert
     timecop (0.9.10)
     tsort (0.2.0)
@@ -106,7 +106,7 @@ DEPENDENCIES
   rubocop-minitest (= 0.38.2)
   rubocop-rake (= 0.7.1)
   simplecov (= 0.22.0)
-  test-unit (= 3.7.1)
+  test-unit (= 3.7.7)
   timecop (= 0.9.10)
   yard (= 0.9.38)