Add buffer time to perf test (#25915)

## Summary & Motivation

As title. This is a consequence of getting rid of the special-purpose
PartitionKeysTimeWindowPartitionsSubset. Long story short, these perf
tests are not very representative of real-world perf scenarios, and
mostly exist as a backstop in case anything massively changes. This
change is also completely irrelevant to the Declarative Automation perf
characteristics, which are more important and have their own separate
perf tests.

TL;DR: We'll probably remove this test in the near future, for now we're
just making it stop failing

## How I Tested These Changes

## Changelog

NOCHANGELOG

integration_tests/test_suites/auto_materialize_perf_tests/test_asset_daemon_perf.py

@@ -66,7 +66,7 @@
     ),
     all_daily_partitioned_500_assets.build_scenario(
         partition_keys_to_backfill=[f"2020-01-{i+1:02}" for i in range(20)],
-        max_execution_time_seconds=30,
+        max_execution_time_seconds=40,
     ),
     all_hourly_partitioned_100_assets.build_scenario(
         partition_keys_to_backfill=["2020-01-01-00:00", "2020-01-02-00:00"],