There aren't any standard ways to simply mark a test as flaky, unfortunately. You need to implement retries internally to the test or catch/handle errors which should not mark the test as failed.
Alternatively, you can mark all of the flaky tests as #[ignore] and use cargo test --include-ignored to, well, include the ignored tests. You can also use --ignored to just run the ignored tests. This only really works if all of your #[ignore]d tests are supposed to be able to be run in this manner.