ci: Run the Android API 21 and FreeBSD 12 jobs on a schedule

Rather than running them on each commit on `main`. This saves resources.

Given that Android API 28 and FreeBSD 13 jobs continue to be run on each
commit on `main`, this seems like an acceptable tradeoff. It’s very
unlikely that a regression will happen which affects the older systems
and *not* the newer systems. If it does, it will be caught within a week
by the scheduled job.

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

.gitlab-ci.yml

@@ -268,7 +268,10 @@ valgrind:
 cross-android_api21_arm64:
   extends:
     - .cross-build-linux
-    - .only-default
+    # The API 28 build is run on each commit, so the API 21 build can be run
+    # less regularly to save CI resources. The chance of a regression on API 21
+    # and not API 28 is tiny.
+    - .only-schedules
   image: $ANDROID_IMAGE
   script:
     # FIXME: add --werror
@@ -377,7 +380,10 @@ vs2017-x64-static:
       - "_build/${env:CI_JOB_NAME}-report.xml"
 
 freebsd-12-x86_64:
-  extends: .only-origin
+  # The FreeBSD 13 build is run on each commit, so the FreeBSD 12 build can be
+  # run less regularly to save CI resources. The chance of a regression on
+  # FreeBSD 12 and not FreeBSD 13 is tiny.
+  extends: .only-schedules
   stage: build
   tags:
     # To run a FreeBSD builder, install gitlab-runner package and start both