Tests: update labgrid to v24.0.1

Bump labgrid to latest release. None of the changes require adjustments in the
tests. Remove pytest from requirements.txt, it's not needed anymore, so let pip
to resolve the correct (latest) version from labgrid's dependencies. With these
new dependencies, previous DeprecationWarnings on Python 3.12 are gone now.

tests/requirements.txt

@@ -1,4 +1,3 @@
-labgrid==23.0.6
-pytest==7.2.2
+labgrid==24.0.1
 pytest-dependency==0.6.0
 pytest-timeout==2.3.1