fix(Turborepo): Disable the new corepack notification (#7901)
### Description
- sets `COREPACK_ENABLE_DOWNLOAD_PROMPT=0` for the integration tests
Newer versions of `corepack` have extra text output when downloading a
version, but the environment variable can disable it
### Testing Instructions
Observe GH Actions integration tests passing.
Closes TURBO-2753
Co-authored-by: Greg Soltis <Greg Soltis>
