chore: add .DS_Store to gitignore

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: lduchosal

.gitignore

@@ -289,3 +289,6 @@ __pycache__/
 *.xsd.cs
 src/System.Net.IPNetwork.TestProject.NetCore/coverage.net5.0.opencover.xml
 coverage.xml
+
+# macOS
+.DS_Store