tests: stabilize test_storage_controller_heartbeats (#9347)

## Problem

This could fail with `reconciliation in progress` if running on a slow
test node such that background reconciliation happens at the same time
as we call consistency_check.

Example:
https://neon-github-public-dev.s3.amazonaws.com/reports/main/11258171952/index.html#/testresult/54889c9469afb232

## Summary of changes

- Call reconcile_until_idle before calling consistency check once,
rather than calling consistency check until it passes

test_runner/regress/test_storage_controller.py

@@ -1300,11 +1300,11 @@ def nodes_online():
     node_to_tenants = build_node_to_tenants_map(env)
     log.info(f"Back online: {node_to_tenants=}")
 
-    # ... expecting the storage controller to reach a consistent state
-    def storage_controller_consistent():
-        env.storage_controller.consistency_check()
+    # ... background reconciliation may need to run to clean up the location on the node that was offline
+    env.storage_controller.reconcile_until_idle()
 
-    wait_until(30, 1, storage_controller_consistent)
+    # ... expecting the storage controller to reach a consistent state
+    env.storage_controller.consistency_check()
 
 
 def test_storage_controller_re_attach(neon_env_builder: NeonEnvBuilder):