Fails when an endpoint has no `requestBody` schema defined

It seems that there has been a change in the OpenAPI spec from GitHub, and the package now fails because an endpoint has a requestBody property but no schema defined.

In this case, it's the `GET /repos/{owner}/{repo}/contents/{path}` endpoint

```
$ VERSION="23.0.0" npm run update-endpoints:fetch-json
> node scripts/update-endpoints/fetch-json.mjs

Downloading releases from https://api.github.com/repos/octokit/openapi/releases?per_page=100&page=1
Downloading releases from https://api.github.com/repos/octokit/openapi/releases?per_page=100&page=2
downloading https://raw.githubusercontent.com/octokit/openapi/v23.0.0/generated/api.github.com.deref.json ...
{
errors: [
TypeError: Cannot read properties of undefined (reading 'oneOf')
at schemaToParameters (file://types.ts/node_modules/github-openapi-graphql-query/lib/schema-to-parameters.js:4:14)
at definitionToEndpoint (file://types.ts/node_modules/github-openapi-graphql-query/lib/definition-to-endpoint.js:66:7)
at schemaToEndpoints (file://types.ts/node_modules/github-openapi-graphql-query/lib/schema-to-endpoints.js:10:24)
at getEndpoints (file://types.ts/node_modules/github-openapi-graphql-query/lib/get-endpoints.js:32:16)
at process.processTicksAndRejections (node:internal/process/task_queues:103:5)
at async Promise.all (index 0)
at async main (file://types.ts/scripts/update-endpoints/fetch-json.mjs:40:18) {
path: [ 'endpoints' ],
locations: [ { line: 3, column: 5 } ],
extensions: [Object: null prototype] {}
}
],
data: null
}
Waiting for the debugger to disconnect...
file://types.ts/scripts/update-endpoints/fetch-json.mjs:48
data: { endpoints },
^

TypeError: Cannot read properties of null (reading 'endpoints')
at main (file://types.ts/scripts/update-endpoints/fetch-json.mjs:48:13)
at process.processTicksAndRejections (node:internal/process/task_queues:103:5)

Node.js v22.22.2
```

```json
{

}

Start by running VERSION="23.0.0" npm run update-endpoints:fetch-json and inspect scripts/update-endpoints/fetch-json.mjs together with the schemaToParameters and definitionToEndpoint stack frames. Trace how the GET /repos/{owner}/{repo}/contents/{path} requestBody is handled when no schema exists. Done means endpoint generation completes without the undefined oneOf error and includes this endpoint correctly.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.