fix: add missing line

Author: D4Vinci

scrapling/engines/_browsers/_stealth.py

@@ -96,6 +96,8 @@ def start(self):
 
             if self._config.cookies:  # pragma: no cover
                 self.context.add_cookies(self._config.cookies)
+
+            self._is_alive = True
         else:
             raise RuntimeError("Session has been already started")
 
@@ -308,6 +310,8 @@ async def start(self):
 
             if self._config.cookies:
                 await self.context.add_cookies(self._config.cookies)  # pyright: ignore
+
+            self._is_alive = True
         else:
             raise RuntimeError("Session has been already started")