ci: cache apk packages

.gitlab-ci.yml

@@ -40,9 +40,12 @@ Check licenses:
 
 Check style:
   variables:
+    APK_CACHE_DIR: ${CI_PROJECT_DIR}/apk-cache
     PRE_COMMIT_HOME: ${CI_PROJECT_DIR}/pre-commit
   before_script:
-    - apk add git pre-commit
+    - mkdir -p "${APK_CACHE_DIR}"
+    - apk update --cache-dir "${APK_CACHE_DIR}"
+    - apk add --cache-dir "${APK_CACHE_DIR}" git pre-commit
   script:
     - pre-commit run --show-diff-on-failure --color=always --all-files
   tags:
@@ -53,11 +56,14 @@ Check style:
     - when: always
   interruptible: true
   cache:
-    key:
-      files:
-        - .pre-commit-config.yaml
-    paths:
-      - ${PRE_COMMIT_HOME}
+    - key: ${CI_COMMIT_REF_SLUG}
+      paths:
+        - ${APK_CACHE_DIR}
+    - key:
+        files:
+          - .pre-commit-config.yaml
+      paths:
+        - ${PRE_COMMIT_HOME}
 
 include:
   - project: "anw_dienste/ci-templates"