fixed datadir related bugs in quantify-scheduler

Explanation of changes

Use a tempdir for tests that require a quantify datadir to be defined. Added fixture for tests that use the pulsar assembler backend.

Motivation of changes

This should fix #65 (closed) .

---

Merge checklist

See also merge request guidelines

• Merge request has been reviewed and approved by a project maintainer.
• Merge request contains a clear description of the proposed changes and the issue it addresses.
• Merge request made onto appropriate branch (develop for most MRs).
• New code is fully tested.
• New code is documented and docstrings use numpydoc format.
• CI pipelines pass
  • black code-formatting passes (gitlab-ci),
  • test suite passes (gitlab-ci),
  • no degradation in code-coverage (codacy),
  • no (serious) new pylint code quality issues introduced (codacy),
  • documentation builds succesfully (readthedocs).