Improve tests and checks workflows

[AmintorDusko]

Issue description

After the recent improvements to build wheels workflows its run time decreased a lot.
Now, tests and checks are the slowest part of the CI/CD pipeline.

• Expected behavior: (What you expect to happen)
  Tests and checks are to be performed in ~< 10 minutes.

• Actual behavior: (What actually happens)
  Some cases can be observed where the run time is > 20 minutes.

• Reproduces how often: (What percentage of the time does it reproduce?)
  Every time a commit is pushed to a PR or a PR is merged. All the time.

• System information: (post the output of import pennylane as qml; qml.about())
  GH runners