Use swh-storage validation proxy.

Required by swh-storage >= v0.0.172.

swh/loader/svn/tests/conftest.py

@@ -31,6 +31,9 @@ def swh_loader_config() -> Dict[str, Any]:
                         'release': 100,
                     },
                 },
+                {
+                    'cls': 'validate'
+                },
                 {
                     'cls': 'memory'
                 },

swh/loader/svn/tests/test_loader.py

@@ -55,6 +55,9 @@ _LOADER_TEST_CONFIG = {
                     'release': 100,
                 },
             },
+            {
+                'cls': 'validate'
+            },
             {
                 'cls': 'memory'
             },