Merge pull request #582 from ruby/dependabot/bundler/test-unit-3.7.6

Bump test-unit from 3.7.3 to 3.7.6

Author: hsbt

Gemfile.lock

@@ -308,7 +308,7 @@ GEM
     sqlite3 (2.9.0-x86_64-linux-gnu)
     sqlite3 (2.9.0-x86_64-linux-musl)
     stringio (3.2.0)
-    test-unit (3.7.3)
+    test-unit (3.7.7)
       power_assert
     thor (1.4.0)
     timeout (0.4.4)