gitlab-ci: cache APKs and git repos between runs

.gitlab-ci.yml

@@ -45,6 +45,7 @@ pages:
   only:
     - schedules
   cache:
+    key: "$CI_JOB_NAME"
     paths:
       - vendor/ruby
   artifacts:
@@ -69,6 +70,11 @@ fdroid-buildserver:
       - unsigned
     expire_in: 1 week
     when: always
+  cache:
+    key: "$CI_JOB_NAME"
+    paths:
+      - build
+      - unsigned
   script:
     - virsh -c qemu:///system destroy builder_default || true
     - virsh -c qemu:///system undefine builder_default