Fix shared default value for headers in BaseDatalabClient (#94)

Author: ml-evs

src/datalab_api/_base.py

@@ -35,7 +35,7 @@ class BaseDatalabClient(metaclass=AutoPrettyPrint):
 
     _api_key: Optional[str] = None
     _session: Optional[httpx.Client] = None
-    _headers: dict[str, str] = {}
+    _headers: dict[str, str]
     _timeout: httpx.Timeout = httpx.Timeout(10.0, read=60.0)
 
     interactive: bool = True
@@ -85,7 +85,7 @@ def __init__(self, datalab_api_url: str, log_level: str = "WARNING"):
         self.log = logging.getLogger(__name__)
 
         self._http_client = httpx.Client
-        self._headers["User-Agent"] = f"Datalab Python API/{__version__}"
+        self._headers = {"User-Agent": f"Datalab Python API/{__version__}"}
 
         self._detect_api_url()