Patch test case on Stdlib/PriorityListTest
Merge branch 'hotfix/#6904-zend-stdlib-priority-list-false-value-support-check' into hotfix/#6904-#6773-zend-stdlib-priority-list-false-value-support

Close #6904
#6904 #6773 - `valid()` should return `true` also for `false` and `null` values in the `PriorityList`
Merge branch 'hotfix/#6904-#6773-zend-stdlib-priority-list-false-value-support' into develop

Close #6904
Forward port #6904