try running tests with two workers

From https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners/about-github-hosted-runners#standard-github-hosted-runners-for-public-repositories
runners have 4 cores (apart from macos-11).

We could use `-n auto`, but I hypothesis that for the e2e tests since we
have one worker process per test process maybe we don't want to actually
use up all the cores with test processes? It doesn't look like it's
possible to tell pytest-xdist to use all core but one, or half the
cores, or anything (issue
herehttps://github.com/pytest-dev/pytest-xdist/issues/477). So lets just
set it to 2 for now which should be a lot faster than 1, if it works.

Author: toofar

.github/workflows/ci.yml

@@ -230,10 +230,10 @@ jobs:
             python -m pip install -U pip
             python -m pip install -U -r misc/requirements/requirements-tox.txt
       - name: "Run ${{ matrix.testenv }}"
-        run: "dbus-run-session -- tox -e ${{ matrix.testenv }} -- ${{ matrix.args }}"
+        run: "dbus-run-session -- tox -e ${{ matrix.testenv }} -- -n 2 ${{ matrix.args }}"
         if: "startsWith(matrix.os, 'ubuntu-')"
       - name: "Run ${{ matrix.testenv }} without DBus"
-        run: "tox -e ${{ matrix.testenv }} -- ${{ matrix.args }}"
+        run: "tox -e ${{ matrix.testenv }} -- -n 2 ${{ matrix.args }}"
         if: "!startsWith(matrix.os, 'ubuntu-')"
       - name: Analyze backtraces
         run: "bash scripts/dev/ci/backtrace.sh ${{ matrix.testenv }}"