gitlab-ci: speed up test runs that do not need git history

GIT_DEPTH sets how many commits of history to clone in CI Jobs.
gitlab.com defaults to 50 with a max of 1000.  The metadata_v0 job is
the only job that needs history, and it needs more than 50.  So this
sets the default to 1, then metadata_v0 to 1000.

https://docs.gitlab.com/ee/ci/pipelines/settings.html#git-shallow-clone

.gitlab-ci.yml

@@ -1,6 +1,8 @@
 
 variables:
   pip: pip3 --timeout 100 --retries 10
+# speed up git checkout phase
+  GIT_DEPTH: 1
 
 
 test:
@@ -22,6 +24,7 @@ test:
 metadata_v0:
   image: registry.gitlab.com/fdroid/ci-images-server:latest
   variables:
+    GIT_DEPTH: 1000
     RELEASE_COMMIT_ID: 37f37ebd88e79ebe93239b72ed5503d5bde13f4b  # 2.0a~
   script:
     - git fetch https://gitlab.com/fdroid/fdroidserver.git $RELEASE_COMMIT_ID