refactor(agent): Drop redundant bool() wrapper around equality check

_is_linuxkit() wrapped a `==` comparison in bool(...), which is a
no-op since == already returns bool.

Refs #11220
Refs #11223

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: rapsealk

src/ai/backend/agent/docker/intrinsic.py

@@ -98,7 +98,7 @@ def _warn_cgroup_fallback_once(plugin: str, container_id: str) -> None:
 
 
 def _is_linuxkit(local_config: Mapping[str, Any]) -> bool:
-    return bool(local_config["agent"]["docker-mode"] == "linuxkit")
+    return cast(str, local_config["agent"]["docker-mode"]) == "linuxkit"
 
 
 # The list of pruned fstype when checking the filesystem usage statistics.