fix(client): revert "send all configured auth headers"

This reverts commit 861ed75.

Author: RobertCraigie

src/finch/_client.py

@@ -147,7 +147,11 @@ def qs(self) -> Querystring:
     @property
     @override
     def auth_headers(self) -> dict[str, str]:
-        return {**self._bearer_auth, **self._basic_auth}
+        if self._bearer_auth:
+            return self._bearer_auth
+        if self._basic_auth:
+            return self._basic_auth
+        return {}
 
     @property
     def _bearer_auth(self) -> dict[str, str]:
@@ -451,7 +455,11 @@ def qs(self) -> Querystring:
     @property
     @override
     def auth_headers(self) -> dict[str, str]:
-        return {**self._bearer_auth, **self._basic_auth}
+        if self._bearer_auth:
+            return self._bearer_auth
+        if self._basic_auth:
+            return self._basic_auth
+        return {}
 
     @property
     def _bearer_auth(self) -> dict[str, str]: