Environmet cache: breaks when using build.tools

[humitos]

We have a half-backed feature called Cache the environment (virtualenv, conda, pip cache, repository) in storage feature that can be enabled via a feature flag. With the usage of build.tools it fails with

$ python -mvirtualenv /home/docs/checkouts/readthedocs.org/user_builds/read-the-docs-test-builds/envs/build-tools 

FileExistsError: [Errno 17] File exists: '/home/docs/.asdf/installs/python/3.10.0/bin/python' -> '/home/docs/checkouts/readthedocs.org/user_builds/read-the-docs-test-builds/envs/build-tools/bin/python' 

Example build (private): https://readthedocs.com/projects/read-the-docs-test-builds/builds/750425/

We haven't used this feature enough yet. We should probably decide first what to do with it: kill it or improve it.

[humitos]

We killed this for now in #8815