Update test-unit to version 3.6.8

Author: depfu[bot]

Gemfile.lock

@@ -218,6 +218,8 @@ GEM
     nio4r (2.7.4)
     nokogiri (1.18.6-arm64-darwin)
       racc (~> 1.4)
+    nokogiri (1.18.6-x86_64-linux-gnu)
+      racc (~> 1.4)
     ostruct (0.6.1)
     parallel (1.26.3)
     parser (3.3.7.2)
@@ -367,6 +369,7 @@ GEM
       simplecov (>= 0.4.1)
     simplecov_json_formatter (0.1.4)
     sqlite3 (2.6.0-arm64-darwin)
+    sqlite3 (2.6.0-x86_64-linux-gnu)
     standard (1.47.0)
       language_server-protocol (~> 3.17.0.2)
       lint_roller (~> 1.0)
@@ -390,7 +393,7 @@ GEM
     stringio (3.1.6)
     terminal-table (4.0.0)
       unicode-display_width (>= 1.1.1, < 4)
-    test-unit (3.6.7)
+    test-unit (3.6.8)
       power_assert
     thor (1.3.2)
     timeout (0.4.3)