ci: Temporarily fold SH and Py checks into style-check job

It doesn’t seem to be possible to use `only:changes` from a branch
pipeline extending `.only-default` and have it correctly trigger when
`*.sh` or `*.py` files are modified.

We possibly need to convert all our pipelines to be merge-request-only,
but that’s an avenue I’ve been down before and I couldn’t get it to
work. Using
[`workflow:rules`](https://docs.gitlab.com/ee/ci/yaml/README.html#workflowrules)
might fix that, but I don’t have time to rework the entire CI to use
that now.

So in the meantime, move the SH and Py checks into the existing
style-check job so we’re not always spinning up two additional container
instances on every merge request.

See !1743.

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>

.gitlab-ci.yml

@@ -40,29 +40,6 @@ variables:
   only:
     - schedules
 
-sh-check:
-  extends: .only-default
-  image: $DEBIAN_IMAGE
-  stage: style-check
-  allow_failure: true
-  script:
-    - .gitlab-ci/run-shellcheck.sh
-  only:
-    changes:
-      - "**/*.sh"
-
-py-check:
-  extends: .only-default
-  image: $DEBIAN_IMAGE
-  stage: style-check
-  allow_failure: true
-  script:
-    - .gitlab-ci/run-black.sh
-    - .gitlab-ci/run-flake8.sh
-  only:
-    changes:
-      - "**/*.py"
-
 style-check-diff:
   extends: .only-default
   image: $DEBIAN_IMAGE
@@ -70,6 +47,9 @@ style-check-diff:
   allow_failure: true
   script:
     - .gitlab-ci/run-style-check-diff.sh
+    - .gitlab-ci/run-shellcheck.sh
+    - .gitlab-ci/run-black.sh
+    - .gitlab-ci/run-flake8.sh
 
 check-todos:
   extends: .only-default