fix schema check for sky spot (skypilot-org#942)

* fix schema check for sky spot

* quote

Author: infwinston

examples/resnet_app.yaml

@@ -2,7 +2,8 @@ name: resnet-app
 
 resources:
   cloud: aws
-  accelerators: V100
+  accelerators:
+    V100: 1
 
 inputs: {
   gs://cloud-tpu-test-dataset/fake_imagenet: 70,

sky/utils/schemas.py

@@ -23,7 +23,16 @@ def get_resources_schema():
                 'type': 'string',
             },
             'accelerators': {
-                'type': 'string',
+                'anyOf': [{
+                    'type': 'string',
+                }, {
+                    'type': 'object',
+                    'required': [],
+                    'maxProperties': 1,
+                    'additionalProperties': {
+                        'type': 'number'
+                    }
+                }]
             },
             'instance_type': {
                 'type': 'string',