Update dependency ajv to v8

Author: renovate[bot]

packages/admin-api-schema/package.json

@@ -26,7 +26,7 @@
   },
   "dependencies": {
     "@tryghost/errors": "^1.2.26",
-    "ajv": "^6.12.6",
+    "ajv": "^8.0.0",
     "lodash": "^4.17.11"
   }
 }

yarn.lock

@@ -3786,7 +3786,7 @@ ajv-formats@~3.0.1:
   dependencies:
     ajv "^8.0.0"
 
-ajv@^6.12.4, ajv@^6.12.6:
+ajv@^6.12.4:
   version "6.12.6"
   resolved "https://registry.npmjs.org/ajv/-/ajv-6.12.6.tgz"
   integrity sha512-j3fVLgvTo527anyYyJOGTYJbG+vnnQYvE0m5mmkc1TK+nxAppkCLMIL0aZ4dblVCNoGShhm+kzE4ZUykBoMg4g==