gitlab CI: use a minimal alpine image for the commit checks

This runs at the same time as the other images being created so it'll fail if
the image itself doesn't exist yet. Since we only need pip here, let's use
alpine and install the two packages we need.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

.gitlab-ci.yml

@@ -130,8 +130,10 @@ variables:
 
 
 check-commit:
-  image: $FEDORA_CONTAINER_IMAGE
+  image: golang:alpine
   stage: prep
+  before_script:
+    - apk add python3 git
   script:
     - pip3 install GitPython
     - pip3 install pytest
@@ -144,7 +146,6 @@ check-commit:
     - master@libinput/libinput
   variables:
     GIT_DEPTH: 100
-    FEDORA_VERSION: 31
   artifacts:
     reports:
       junit: results.xml