fix(tests): improve test_scrubber_tenant_snapshot stability (#11471)

## Problem
`test_scrubber_tenant_snapshot` is flaky with `request was dropped`
errors. More details are in the issue.
- Closes: https://github.com/neondatabase/neon/issues/11278

## Summary of changes
- Disable shard scheduling during pageservers restart
- Add `reconcile_until_idle` in the end of the test

storage_controller/src/service.rs

@@ -7270,7 +7270,7 @@ impl Service {
             }
 
             // Eventual consistency: if an earlier reconcile job failed, and the shard is still
-            // dirty, spawn another rone
+            // dirty, spawn another one
             if self
                 .maybe_reconcile_shard(shard, &pageservers, ReconcilerPriority::Normal)
                 .is_some()