Move GitHub Token export to backend (#6153)

Co-authored-by: openhands <openhands@all-hands.dev>

openhands/server/session/agent_session.py

@@ -180,6 +180,13 @@ class AgentSession:
 
         logger.debug(f'Initializing runtime `{runtime_name}` now...')
         runtime_cls = get_runtime_cls(runtime_name)
+        env_vars = (
+            {
+                'GITHUB_TOKEN': github_token,
+            }
+            if github_token
+            else None
+        )
         self.runtime = runtime_cls(
             config=config,
             event_stream=self.event_stream,
@@ -187,6 +194,7 @@ class AgentSession:
             plugins=agent.sandbox_plugins,
             status_callback=self._status_callback,
             headless_mode=False,
+            env_vars=env_vars,
         )
 
         # FIXME: this sleep is a terrible hack.