Enable unit-test-long-bucket tasks in patch builds

In WT-9853 a set of unit-test-long-bucket?? was introduced. Those tasks are aimed to be included in the pre-merge testing (i.e. commit-queue patch builds). However, they were not added to any build variant, making it impossible to run. 

As we don't hope the set of tasks to run in commit builds (the unit-test-long task covers the same testing scope), we can try to use the "patch_only: true" parameter to config the set of tasks.