ci/docker: Clear the results file before starting a new deqp test run.

crocus-hsw was failing because results.csv.zst was left around in the
results dir, and then zstd -o complained.  We shouldn't be uploading stale
results files, anyway, so do an rm -rf first to clean up when the docker
container gets reused.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25509>

.gitlab-ci/test/gitlab-ci.yml

@@ -154,6 +154,7 @@ clang-format:
 
 .deqp-test:
   script:
+    - rm -rf results # Clear out old results if the docker container was cached
     - ./install/deqp-runner.sh
   artifacts:
     exclude: