Fix: project v2 item field change type may be labels

[jecluis]

According to the webhook events we're getting sent by github, the changed field_type can be "labels" as well, but this doesn't seem to be covered by the octokit schema.

As an example, take the following snippet:

"action": "edited",
    "projects_v2_item": {
      "id": 12345,
      "node_id": "PVTI_ASDASD",
      "project_node_id": "PVT_ASDASD",
      "content_node_id": "I_ASDASD",
      "content_type": "Issue",
      "creator": {
        "login": "jecluis",
        [...]
      },
      "created_at": "2023-12-18T06:44:23Z",
      "updated_at": "2023-12-18T16:21:38Z",
      "archived_at": null
    },
    "changes": {
      "field_value": {
        "field_node_id": "PVTF_ASDASD",
        "field_type": "labels"
      }
    },

Signed-off-by: Joao Eduardo Luis <joao@1e3ms.io>

[yanyongyu]

it seems this field value is not documented in the webhook types... But, the latest openapi description mark this field as simple string instead of enum. I'm working on migrate the codegen to using the openapi instead of octokit #67 . just make a fix currently 🤔 .

[jecluis]

Fixes applied, sorry for the silly mistake. Thanks @yanyongyu !