test_runner/performance: skip test_bulk_insert (#7238)

## Problem
`test_bulk_insert` becomes too slow, and it fails constantly:
https://github.com/neondatabase/neon/issues/7124

## Summary of changes
- Skip `test_bulk_insert` until it's fixed

test_runner/performance/test_bulk_insert.py

@@ -1,5 +1,6 @@
 from contextlib import closing
 
+import pytest
 from fixtures.benchmark_fixture import MetricReport
 from fixtures.compare_fixtures import NeonCompare, PgCompare
 from fixtures.pageserver.utils import wait_tenant_status_404
@@ -17,6 +18,7 @@ from fixtures.types import Lsn
 # 3. Disk space used
 # 4. Peak memory usage
 #
+@pytest.mark.skip("See https://github.com/neondatabase/neon/issues/7124")
 def test_bulk_insert(neon_with_baseline: PgCompare):
     env = neon_with_baseline