Reenable tests for demo-server docker image after some investigation

[agoscinski]

Currently the tests fail that use the demo server docker image

aiida-firecrest/.github/workflows/server-tests.yml

Lines 42 to 44 in eb7f751

	repository: eth-cscs/firecrest
	ref: ${{ matrix.firecrest-version }}
	path: .demo-server

So they have been disabled in PR #36. This needs some further investigation and most probably some work on eth-cscs side to fix it until it can be again enabled.

For the moment we run the tests locally with a real server.