test: disable large slru basebackup bench in ci (#7025)

The test is flaky due to
https://github.com/neondatabase/neon/issues/7006.

test_runner/performance/pageserver/pagebench/test_large_slru_basebackup.py

@@ -1,5 +1,6 @@
 import asyncio
 import json
+import os
 from pathlib import Path
 from typing import Any, Dict, Tuple
 
@@ -19,6 +20,10 @@ from performance.pageserver.util import (
 @pytest.mark.parametrize("n_tenants", [10])
 @pytest.mark.parametrize("get_vectored_impl", ["sequential", "vectored"])
 @pytest.mark.timeout(1000)
+@pytest.mark.skipif(
+    os.getenv("CI", "false") == "true",
+    reason="The test if flaky on CI: https://github.com/neondatabase/neon/issues/7006",
+)
 def test_basebackup_with_high_slru_count(
     neon_env_builder: NeonEnvBuilder,
     zenbenchmark: NeonBenchmarker,