Quarantine a flaky test

The `Gitlab::Database::Partitioning::IntRangeStrategy#missing_partitions when the current partitions are not completed when partitions have data returns missing partitions`
test has either ~"flakiness::1" or ~"flakiness::2" label set, which means the number of reported failures
is at or above 95 percentile, indicating unusually high failure count.

This MR quarantines the test. This is a discussion starting point to let the
responsible group know about the flakiness so that they can take action:

- accept the merge request and schedule the associated issue to improve the test
- close the merge request in favor of another merge request to delete the test

Please follow the
[Flaky tests management process](https://handbook.gitlab.com/handbook/engineering/infrastructure/engineering-productivity/flaky-tests-management-and-processes/#flaky-tests-management-process)
to help us increase `master` stability.

Please let us know your feedback
[in the dedicated issue](https://gitlab.com/gitlab-org/quality/engineering-productivity/team/-/issues/447).

Related to https://gitlab.com/gitlab-org/gitlab/-/issues/444872.

This change was generated by
[gitlab-housekeeper](https://gitlab.com/gitlab-org/gitlab/-/tree/master/gems/gitlab-housekeeper)
using the Keeps::QuarantineFlakyTests keep.

To provide feedback on your experience with `gitlab-housekeeper` please comment in
<https://gitlab.com/gitlab-org/gitlab/-/issues/442003>.

Changelog: other

spec/lib/gitlab/database/partitioning/int_range_strategy_spec.rb

@@ -106,7 +106,7 @@
           model.create!(external_id: 15)
         end
 
-        it 'returns missing partitions' do
+        it 'returns missing partitions', quarantine: 'https://gitlab.com/gitlab-org/gitlab/-/issues/444872' do
           expect(missing_partitions.size).to eq(7)
 
           expect(missing_partitions).to include(