ci(tests): Use -n auto from pytest-xdist

Author: tony

.github/workflows/tests.yml

@@ -71,7 +71,7 @@ jobs:
           export PATH=$HOME/tmux-builds/tmux-${{ matrix.tmux-version }}/bin:$PATH
           ls $HOME/tmux-builds/tmux-${{ matrix.tmux-version }}/bin
           tmux -V
-          poetry run py.test --cov=./ --cov-append --cov-report=xml
+          poetry run py.test --cov=./ --cov-append --cov-report=xml -n auto
         env:
           COV_CORE_SOURCE: .
           COV_CORE_CONFIG: .coveragerc