Merge pull request #633 from ruby/dependabot/bundler/test-unit-3.7.8

Bump test-unit from 3.7.7 to 3.7.8

Author: hsbt

Gemfile.lock

@@ -310,7 +310,7 @@ GEM
     sqlite3 (2.9.5-x86_64-linux-gnu)
     sqlite3 (2.9.5-x86_64-linux-musl)
     stringio (3.2.0)
-    test-unit (3.7.7)
+    test-unit (3.7.8)
       power_assert
     thor (1.5.0)
     timeout (0.6.1)