test: fix test_pageserver_recovery flakyness (#7207)

## Problem
We recently introduced log file validation for the storage controller.
The heartbeater will WARN when it fails
for a node, hence the test fails.

Closes https://github.com/neondatabase/neon/issues/7159

## Summary of changes
* Warn only once for each set of heartbeat retries
* Allow list heartbeat warns

control_plane/attachment_service/src/heartbeater.rs

@@ -139,7 +139,7 @@ impl HeartbeaterTask {
                         .with_client_retries(
                             |client| async move { client.get_utilization().await },
                             &jwt_token,
-                            2,
+                            3,
                             3,
                             Duration::from_secs(1),
                             &cancel,

test_runner/regress/test_recovery.py

@@ -15,6 +15,13 @@ def test_pageserver_recovery(neon_env_builder: NeonEnvBuilder):
     env = neon_env_builder.init_start()
     env.pageserver.is_testing_enabled_or_skip()
 
+    # We expect the pageserver to exit, which will cause storage storage controller
+    # requests to fail and warn.
+    env.storage_controller.allowed_errors.append(".*management API still failed.*")
+    env.storage_controller.allowed_errors.append(
+        ".*Reconcile error.*error sending request for url.*"
+    )
+
     # Create a branch for us
     env.neon_cli.create_branch("test_pageserver_recovery", "main")