\a is not a valid ECMA 262 regex.

Draft 2020-12 now references the ECMA 262 11.0 specification, and
thereby does not allow \a.

Refs: json-schema-org/json-schema-spec#821
Closes: #309

Author: Julian

tests/draft-next/optional/ecmascript-regex.json

@@ -383,6 +383,17 @@
             }
         ]
     },
+    {
+        "description": "\\a is not an ECMA 262 control escape",
+        "schema": { "$ref": "https://json-schema.org/draft/next/schema" },
+        "tests": [
+            {
+                "description": "when used as a pattern",
+                "data": { "pattern": "\\a" },
+                "valid": false
+            }
+        ]
+    },
     {
         "description": "unicode digits are more than 0 through 9",
         "schema": { "pattern": "^\\p{digit}+$" },

tests/draft2020-12/optional/ecmascript-regex.json

@@ -383,6 +383,17 @@
             }
         ]
     },
+    {
+        "description": "\\a is not an ECMA 262 control escape",
+        "schema": { "$ref": "https://json-schema.org/draft/2020-12/schema" },
+        "tests": [
+            {
+                "description": "when used as a pattern",
+                "data": { "pattern": "\\a" },
+                "valid": false
+            }
+        ]
+    },
     {
         "description": "unicode digits are more than 0 through 9",
         "schema": { "pattern": "^\\p{digit}+$" },