Reactivate page bench test in CI after ignoring CopyFail error in pageserver (#8023)

## Problem

Testcase page bench test_pageserver_max_throughput_getpage_at_latest_lsn
had been deactivated because it was flaky.

We now ignore copy fail error messages like in


https://github.com/neondatabase/neon/blob/270d3be507643f068120b52838c497f6c1b45b61/test_runner/regress/test_pageserver_getpage_throttle.py#L17-L20

and want to reactivate it to see it it is still flaky

## Summary of changes

- reactivate the test in CI
- ignore CopyFail error message during page bench test cases

## Checklist before requesting a review

- [ ] I have performed a self-review of my code.
- [ ] If it is a core feature, I have added thorough tests.
- [ ] Do we need to implement analytics? if so did you add the relevant
metrics to the dashboard?
- [ ] If this PR requires public announcement, mark it with
/release-notes label and add several sentences in this section.

## Checklist before merging

- [ ] Do not forget to reformat commit message to not include the above
checklist

test_runner/performance/pageserver/pagebench/test_pageserver_max_throughput_getpage_at_latest_lsn.py

@@ -1,5 +1,4 @@
 import json
-import os
 from pathlib import Path
 from typing import Any, Dict, Tuple
 
@@ -35,10 +34,6 @@ from performance.pageserver.util import (
 @pytest.mark.timeout(
     10000
 )  # TODO: this value is just "a really high number"; have this per instance type
-@pytest.mark.skipif(
-    os.getenv("CI", "false") == "true",
-    reason="The test if flaky on CI: https://github.com/neondatabase/neon/issues/6724",
-)
 def test_pageserver_max_throughput_getpage_at_latest_lsn(
     neon_env_builder: NeonEnvBuilder,
     zenbenchmark: NeonBenchmarker,
@@ -91,6 +86,14 @@ def test_pageserver_max_throughput_getpage_at_latest_lsn(
         n_tenants,
         setup_wrapper,
     )
+
+    env.pageserver.allowed_errors.append(
+        # https://github.com/neondatabase/neon/issues/6925
+        # https://github.com/neondatabase/neon/issues/6390
+        # https://github.com/neondatabase/neon/issues/6724
+        r".*query handler for.*pagestream.*failed: unexpected message: CopyFail during COPY.*"
+    )
+
     run_benchmark_max_throughput_latest_lsn(env, pg_bin, record, duration)