make rest api example pipeline also work without a token

dlt/sources/rest_api_pipeline.py

@@ -1,4 +1,4 @@
-from typing import Any
+from typing import Any, Optional
 
 import dlt
 from dlt.common.pendulum import pendulum
@@ -11,16 +11,21 @@
 
 
 @dlt.source(name="github")
-def github_source(access_token: str = dlt.secrets.value) -> Any:
+def github_source(access_token: Optional[str] = dlt.secrets.value) -> Any:
     # Create a REST API configuration for the GitHub API
     # Use RESTAPIConfig to get autocompletion and type checking
     config: RESTAPIConfig = {
         "client": {
             "base_url": "https://api.github.com/repos/dlt-hub/dlt/",
-            # "auth": {
-            #     "type": "bearer",
-            #     "token": access_token,
-            # },
+            # we add an auth config if the auth token is present
+            "auth": (
+                {
+                    "type": "bearer",
+                    "token": access_token,
+                }
+                if access_token
+                else None
+            ),
         },
         # The default configuration for all resources and their endpoints
         "resource_defaults": {