chore: git ignore unwanted package managers (#214)

https://github.com/openai/codex/blob/main/package-lock.json

Considering that the current repository uses `npm` as the package
manager, the related files for `yarn` and `pnpm` are therefore ignored.

.gitignore

@@ -55,3 +55,8 @@ Thumbs.db
 Icon?
 .Spotlight-V100/
 
+# Unwanted package managers
+.yarn/
+yarn.lock
+pnpm-lock.yaml
+