Fix import for new moto version

Moto 5 (which supports py38+) replaces all decorators with `mock_aws`.

tests/unit/test_storage.py

@@ -1,3 +1,4 @@
+import sys
 import uuid
 
 import pytest
@@ -12,7 +13,12 @@
 
 try:
     import boto3
-    from moto import mock_s3
+
+    if sys.version_info >= (3, 8):
+        from moto import mock_aws as moto_mock
+    else:
+        # moto v5 doesn't support py37; fall back to v4 with mock_s3
+        from moto import mock_s3 as moto_mock
 
     has_boto = True
 except ImportError:
@@ -32,7 +38,7 @@ def __init__(self):
 
 @pytest.fixture
 def test_bucket_mock():
-    with mock_s3():
+    with moto_mock():
         res = boto3.client("s3")
         res.create_bucket(Bucket="compute-test-1")
         yield