fix: export detect_gce_residency_linux function (#1403)

Author: arithmetic1728

google/auth/compute_engine/__init__.py

@@ -14,8 +14,9 @@
 
 """Google Compute Engine authentication."""
 
+from google.auth.compute_engine._metadata import detect_gce_residency_linux
 from google.auth.compute_engine.credentials import Credentials
 from google.auth.compute_engine.credentials import IDTokenCredentials
 
 
-__all__ = ["Credentials", "IDTokenCredentials"]
+__all__ = ["Credentials", "IDTokenCredentials", "detect_gce_residency_linux"]