chore: Add .yarn/sdks to .gitignore

According to https://yarnpkg.com/getting-started/qa/#which-files-should-be-gitignored it is optional to keep the editor SDKs in the repository. Let's not keep them here so that every contributor can set up whatever SDKs they require.

See https://yarnpkg.com/getting-started/editor-sdks/ for more info on yarn editor SDKs. Note that we're currently not using yarn PnP package resolution, so most editors should work without any SDKs configured.