refactor: consolidate SandboxClient import into single if/else block

Co-authored-by: gemini-code-assist[bot] <176aborting...@users.noreply.github.com>

Author: leslyarun

src/google/adk/code_executors/gke_code_executor.py

@@ -29,13 +29,13 @@
 from .code_execution_utils import CodeExecutionInput
 from .code_execution_utils import CodeExecutionResult
 
-try:
-  from k8s_agent_sandbox import SandboxClient
-except ImportError:
-  SandboxClient = None
-
 if TYPE_CHECKING:
   from k8s_agent_sandbox import SandboxClient
+else:
+  try:
+    from k8s_agent_sandbox import SandboxClient
+  except ImportError:
+    SandboxClient = None
 
 # Expose these for tests to monkeypatch.
 client = k8s.client