Add test cases for a list of platform builders

Author: shanejbrown

tests/test_config_validation/test_global_config.py

@@ -120,6 +120,33 @@ def fixture_override_master_config_file(tmp_path):
                 "disable-multi-platform:  Input should be a valid boolean, unable to interpret input (bool_parsing)"
             ],
         ),
+        (
+            """
+          platform-builders:
+            linux/amd64:
+              - builder1
+              - builder2
+            linux/arm64:
+              - builder3
+          """,
+            [],
+        ),
+        (
+            """
+          platform-builders:
+            linux/amd64: builder2
+            linux/arm64: builder3
+          """,
+            [],
+        ),
+        (
+            """
+          platform-builders:
+            - builder2
+            - builder3
+          """,
+            ["platform-builders:  Input should be a valid dictionary (dict_type)"],
+        ),
     ],
 )
 def test_config_data(