stop using cache on tox workdir

With the newer runner, the tests tend to fail

.gitlab-ci.yml

@@ -71,7 +71,7 @@
   stage: test
   image: quay.orus.io/xcg/multi-python
   script:
-    - tox --workdir=.cache/tox --parallel all -e
+    - tox --parallel all -e
       36,py37,py38,py39,py310,py311,py312,coverage-report,coverage-xml
   artifacts:
     when: always