CI: Remove pytest-xdist and pytest-rerunfailures options from addopts and only add them in CI jobs

[seisman]

Description of proposed changes

In PR #3193, pytest-xdist and pytest-rerunfailures were added to speed up the CI jobs. They work well but also cause some troubles:

1. Options -n auto --reruns 2 are added to addopts, so pytest-xdist and pytest-rerunfailures are required in local environments.
2. In local environments, I (maybe also others) usually don't run the full tests and only run a few specific tests, but pytest-xdist's -n auto option always initializes multiple workers, which takes more time when running a single test.

This PR removes the options -n auto --reruns 2 from pyproject.toml and add the options to the workflows if needed.