### Why?
Since dep installation within next-codemod runs `pnpm install` on the
Next.js repo, it installs in the workspace root scope during testing. We
could add a layer for testing like adding a flag `--no-workspace`, but
it will reduce confidence between the actual running and testing.
Therefore added an empty `pnpm-workspace.yaml` file to each fixture.
### How?
By doing this, both installation and testing will have same environment
of running, `pnpm install` only. To prevent created `pnpm-lockfile` to
be shipped, gitignored it.
This way, we keep things simple and make sure tests match real-world use
better. The empty `pnpm-workspace.yaml` files make `pnpm` treat each
fixture separately, which is closer to how it'll work for users.
Jiwon Choi