Add .credentials.json to .gitignore

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <[email protected]>

Author: gfraiteur

.gitignore

@@ -18,4 +18,4 @@ global.json
 eng/docker-context/claude.json
 scripts/build-agents/last-execution.txt
 *.log
-copilot.data.*
+copilot.data.*eng/docker-context/.credentials.json