CI: add distfile-check (MR 1388)

Verify that each distfile has the same hash in a directory full of APKBUILDs.

I've considered merging the new job with aports-static, but since there
are quite a few setup steps, it would make the .gitlab-ci.yml less
readable.

Related: https://gitlab.com/postmarketOS/ci-common/-/blob/master/distfile-check/README.md

.gitlab-ci.yml

@@ -80,6 +80,18 @@ aports-static:
       - pmbootstrap.cfg
     expire_in: 1 week
 
+distfile-check:
+  stage: first
+  <<: *only-default
+  before_script:
+    - apk -q add make findutils
+    - wget "https://gitlab.com/postmarketOS/ci-common/-/archive/master/ci-common-master.tar.bz2"
+    - tar -xf ci-common-master.tar.bz2
+    - mv ci-common-master/distfile-check/*.sh ci-common-master/distfile-check/Makefile .
+    - rm -r ci-common-master ci-common-master.tar.bz2
+  script:
+    - make -j999
+
 # APKBUILD linting
 aport-lint:
   stage: first