GitHub comments_url Swagger metadata incorrectly describes Diff URL

## Problem

The pinned managed GitHub connector Swagger gives `PullRequest.comments_url` the same metadata as `diff_url`:

```json
"comments_url": {
"type": "string",
"format": "uri",
"x-ms-summary": "Pull Request Diff Url",
"description": "The Diff URL for the pull request."
}
```

The C# collision fix correctly preserves both wire fields, mapping `diff_url` to `DiffUrl` and `comments_url` to `PullRequestDiffUrl`, but the generated XML summary for `PullRequestDiffUrl` remains misleading because documentation is emitted from this owner metadata.

## Expected

Correct the managed connector Swagger metadata for `PullRequest.comments_url` to describe the comments URL, then regenerate the GitHub client. Do not hand-edit the generated SDK file.

## References

- Found during review of #246
- Generator collision fix: AzureUX-BPM PR 16763267
- Pinned Swagger cache SHA-256: `ab508ed2ea1f9c4cf3216d440e2d50cf86b3cc0f5312fa39ee036185d493c73e`

Inspect the pinned managed GitHub connector Swagger and the PullRequest.comments_url owner metadata first. Correct its summary and description, regenerate the GitHub client as requested, and verify that the generated XML describes the comments URL while diff_url and comments_url remain distinct wire fields.

Written by the indexing model from the issue text.