Add .pnpm-store to .gitignore (#43366)

pnpm creates this folder in the root of the project
when running this repo in a docker (because it needs to create this on the same device and the project is mounted into the container as a new device)

This is a follow-up on #43138

I added this into my personal `.git/info/exclude` and forgot to include this change with that PR.



## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see [`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] [e2e](https://github.com/vercel/next.js/blob/canary/contributing/core/testing.md#writing-tests-for-nextjs) tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see [`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm build && pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)

.gitignore

@@ -10,6 +10,7 @@ package-lock.json
 yarn.lock
 !/yarn.lock
 test/node_modules
+.pnpm-store/
 
 # logs & pids
 *.log