fix: Fix regression in v0.52.0 where the auth attribute was removed from the RESTStream.requests_session instance (#3343)

* fix: Fix regression in v0.52.0 where the `auth` attribute was removed from the `RESTStream.requests_session` instance

* Fix tests

Author: edgarrmondragon

singer_sdk/streams/rest.py

@@ -393,6 +393,7 @@ def build_prepared_request(
             A :class:`requests.PreparedRequest` object.
         """
         request = requests.Request(*args, **kwargs)
+        self.requests_session.auth = self.authenticator
         return self.requests_session.prepare_request(request)
 
     def prepare_request(

tests/core/rest/test_authenticators.py

@@ -277,8 +277,6 @@ def test_requests_library_auth(rest_tap: Tap):
     """Validate that a requests.auth object can be used as an authenticator."""
     stream = t.cast("RESTStream", rest_tap.streams["proxy_auth_stream"])
     request = stream.prepare_request(None, None)
-    assert "Proxy-Authorization" not in request.headers
-
     authenticated_request = stream.authenticator(request)
     assert "Proxy-Authorization" in authenticated_request.headers
 
@@ -590,8 +588,8 @@ def backoff_jitter(self, value: float) -> float:
     # Verify the request succeeded
     assert records == [{"id": 1}]
 
-    # Verify authenticator was called 3 times (initial + 2 retries)
-    assert auth_call_count == 3
+    # Verify authenticator was called 4 times (setup + initial + 2 retries)
+    assert auth_call_count == 4
 
     assert len(caplog.records) == 2
     assert all(rec.levelname == "ERROR" for rec in caplog.records)