chore: ignore claude plugin format (ChromeDevTools#1784)

When release please tries to update the version it change the format
which then fails CI check,
We can safely ignore the formatting for that file.

Author: Lightning00Blade

.prettierignore

@@ -1,3 +1,6 @@
 # Prettier-only ignores.
 CHANGELOG.md
-src/third_party/lighthouse-devtools-mcp-bundle.js
+src/third_party/lighthouse-devtools-mcp-bundle.js
+
+# Release-please formatting brakes CI checks
+.claude-plugin/plugin.json