Ignore in-tree pnpm store

[yorickdewid]

Reasons for making this change

Under some conditions (when there is no user directory or inside a dev container) the pnpm store is placed inside the source tree.

Links to documentation supporting these rule changes

https://pnpm.io/settings#store-settings

If this is a new template

https://pnpm.io

Merge and Approval Steps

• [ ] Confirm that you've read the contribution guidelines and ensured your PR aligns
• [ ] Ensure CI is passing
• [ ] Get a review and Approval from one of the maintainers

[yorickdewid]

Possible duplicate of #4707

[github-actions[bot]]

This PR is stale because there have been no updates in 90 days. It will close after 180 days of inactivity. Leave a comment if you want to keep it open :smile: