refactor(.github/workflows): reorganize many builds (#332)

1. reduce the number of periodic builds

2. just build as part of the release process in most cases

3. shorttests duplicates coverage

Preliminary changes as part of https://github.com/ooni/probe/issues/1466

.github/workflows/android.yml

@@ -1,10 +1,9 @@
-# android verifies we can still build for Android
+# android checks whether we can build for Android
 name: android
 on:
   push:
     branches:
       - "release/**"
-      - "master"
 jobs:
   test:
     runs-on: ubuntu-20.04