[HOTFIX] wrong image for testing

.gitlab-ci.yml

@@ -77,6 +77,7 @@ coverage:
 
 python38:
   stage: test
+  image: python:3.8
   script:
     - pytest tests dios/test -Werror --junitxml=report.xml
     - python -m saqc --config docs/resources/data/config.csv --data docs/resources/data/data.csv --outfile /tmp/test.csv