Labels are not being applied from config JSON

### TL;DR

```json
{
"$schema": "https://raw.githubusercontent.com/googleapis/release-please/main/schemas/config.json",
"packages": {
".": {}
},
"pull-request-title-pattern": "chore(${scope}): release${component} ${version}",
"extra-label": "Type: chore, Type: Docs",
"extra-files": [
"CHANGELOG.md"
]
}
```

Above `release-please-config.json` does not allow inclusion or addition of custom labels specified.

### Expected behavior

Expect the PR to have additional labels specified in the default config file.

### Observed behavior

Custom user labels are not added to the label, rather standard `autopending` label is attached to the PR.

### Action YAML

```yaml
name: Automated release
run-name: Executing release on ${{ github.repository }} 🚀

on:
push:
branches: [main]

permissions:
contents: write
pull-requests: write

jobs:
# 1. `package.json`, `README.md` and `CHANGELOG.md` updates
release:
name: Release setup 🔧
runs-on: ubuntu-latest
steps:
- name: Release version ⚡️
uses: google-github-actions/release-please-action@v4
with:
token: ${{ secrets.RELEASE_TOKEN }}
release-type: node
target-branch: main
```

### Log output

_No response_

### Additional information

_No response_

Reproduce the issue using the shown release-please-config.json and release-please-action@v4 workflow, with extra-label set to the two custom labels. Inspect how the action reads that configuration and verify that a generated pull request receives the configured labels rather than only autopending; the issue has no log or test path to guide further investigation.

Written by the indexing model from the issue text.