ajv request body validation regression following an upgrade to @loopback/rest 15.0.3

Describe the bug

Since after upgrading to @loopback/rest 15.0.3 , ajv request body validation fail when the schema contain the "discriminator" key word.

Logs

equest POST /accounts/7342217301273/actions failed with status code 500. Error: strict mode: unknown keyword: "discriminator"
    at checkStrictMode (/home/fidgi/my-app/node_modules/ajv/lib/compile/util.ts:211:28)
    at checkUnknownRules (/home/fidgi/my-app/node_modules/ajv/lib/compile/util.ts:27:22)
    at checkKeywords (/home/fidgi/my-app/node_modules/ajv/lib/compile/validate/index.ts:153:20)
    at validateFunctionCode (/home/fidgi/my-app/node_modules/ajv/lib/compile/validate/index.ts:40:5)
    at Ajv.compileSchema (/home/fidgi/my-app/node_modules/ajv/lib/compile/index.ts:163:25)
    at Ajv._compileSchemaEnv (/home/fidgi/my-app/node_modules/ajv/lib/core.ts:737:24)
    at Ajv.compile (/home/fidgi/my-app/node_modules/ajv/lib/core.ts:389:34)
    at createValidator (/home/fidgi/my-app/node_modules/@loopback/rest/src/validation/request-body.validator.ts:236:18)
    at validateValueAgainstSchema (/home/fidgi/my-app/node_modules/@loopback/rest/src/validation/request-body.validator.ts:153:16)
    at validateRequestBody (/home/fidgi/my-app/node_modules/@loopback/rest/src/validation/request-body.validator.ts:76:9)
    at buildOperationArguments (/home/fidgi/my-app/node_modules/@loopback/rest/src/parser.ts:92:28)
    at processTicksAndRejections (node:internal/process/task_queues:95:5)
    at async MySequence.handle (/home/fidgi/my-app/src/sequence.ts:51:20)
    at async HttpHandler._handleRequest (/home/fidgi/my-app/node_modules/@loopback/rest/src/http-handler.ts:115:5)

Additional information

This seems to be related to this commit

Reproduction

n/a

Start with the linked commit and the validation flow in @loopback/rest/src/validation/request-body.validator.ts, especially createValidator and validateValueAgainstSchema. Reproduce the request-body schema failure with the discriminator keyword, then verify that validation no longer rejects it after the regression is addressed.