ci: run python tests only when python code changes

.gitlab-ci.yml

@@ -15,10 +15,16 @@ check-manifest:
 
 flake8:
   stage: tests
+  rules:
+    - changes:
+        - "**/*.py"
   script: tox -e flake8
 
 py3:
   stage: tests
+  rules:
+    - changes:
+        - "**/*.py"
   script: tox -e py3
   artifacts:
     paths:
@@ -26,6 +32,9 @@ py3:
 
 black:
   stage: tests
+  rules:
+    - changes:
+        - "**/*.py"
   script: tox -e black
 
 mypy: