fix: Remove check on serving_container_image_uri when artifact_uri and local_model is given

COPYBARA_INTEGRATE_REVIEW=#4558 from rragundez:patch-1 d7ff12e
PiperOrigin-RevId: 696672287

Author: rragundez

google/cloud/aiplatform/models.py

@@ -5020,7 +5020,9 @@ def upload(
             if not model_dir.exists():
                 raise ValueError(f"artifact_uri path does not exist: '{artifact_uri}'")
             PREBUILT_IMAGE_RE = "(us|europe|asia)-docker.pkg.dev/vertex-ai/prediction/"
-            if re.match(PREBUILT_IMAGE_RE, serving_container_image_uri):
+            if serving_container_image_uri and re.match(
+                PREBUILT_IMAGE_RE, serving_container_image_uri
+            ):
                 if not model_dir.is_dir():
                     raise ValueError(
                         f"artifact_uri path must be a directory: '{artifact_uri}' when using prebuilt image '{serving_container_image_uri}'"