Revert "Run Unit tests for all branches again"

This reverts commit 71d3fa5.

Author: Michael Vasseur

gitlab/ci/unit.yml

@@ -29,12 +29,21 @@
         - unit-tests.xml
 
 run unit tests:
+  only:
+    - main
+    - /^[0-9].[0-9]$/
   extends: [.mariadb_job,.phpsupported_job,.unit_job]
 
 run unit tests (PR):
+  except:
+    - main
+    - /^[0-9].[0-9]$/
   extends: [.mariadb_job,.phpsupported_job_pr,.unit_job]
 
 run unit tests (MySQL):
+  only:
+    - main
+    - /^[0-9].[0-9]$/
   extends: [.mysql_job,.unit_job]
   parallel:
     matrix: