restrict date regex to only valid months; fixes #310

Author: kbroch-rivosinc

schemas/ext_schema.json

@@ -147,7 +147,8 @@
               },
               "ratification_date": { 
                 "oneOf": [
-                  {"type": "string", "pattern": "^20[0-9][0-9]-[0-9][0-9]$", "$comment": "When ratification date is known" },
+                  {"type": "string", "pattern": "^20[0-9][0-9]-[0-1][0-2]$", "$comment": "When ratification date is known", 
+                  "description": "<4 digit year>-<2 digit month>", "examples": ["2019-01", "2024-12"] },
                   {"type": "string", "pattern": "^unknown$", "$comment": "When ratification date is unknown" },
                   {"type": "null", "$comment": "When version isn't ratified" }
                 ]