Reintroduce aiida-test-cache dependency in pyproject.toml

[PhilippRue]

Currently aiida-test-cache is under development and doesn't have a stable release we can use. So I use a forked version which, however, cannot be in the dependency list when trying to publish it on pypi.

Fix this later when the aiida-test-cache release is there.

Things to do:

• update testing extra dependencies with aiida-test-cache
• update ci.yml and cd.yml in .github/workflows
• create release