Revert "ci: Run fuzzer task for the master branch only"

This reverts commit 5a9e255e5a.

.cirrus.yml

@@ -237,7 +237,6 @@ task:
 
 task:
   name: '[fuzzer,address,undefined,integer, no depends] [focal]'
-  only_if: $CIRRUS_BRANCH == $CIRRUS_DEFAULT_BRANCH || $CIRRUS_BASE_BRANCH == $CIRRUS_DEFAULT_BRANCH
   << : *GLOBAL_TASK_TEMPLATE
   container:
     image: ubuntu:focal