Do not save pip cache when using CACHED_ENVIRONMENT
Do not save pip cache when using CACHED_ENVIRONMENT

Saving these files in the tarfile will push/pull on every build and
it's useless because if we are saving the environment already, these
packages will be already installed there. So, there is no need to keep
them in the tarfile to not use them after all.

rtfd/readthedocs.org,rtfd/readthedocs.org,rtfd/readthedocs.org,rtfd/readthedocs.org