Grant dependabot write permissions on PR events.

[yswe]

It seems the workflow needs explicit permissions to push commits:

remote: Permission to GoogleCloudPlatform/gke-networking-api.git denied to github-actions[bot]. fatal: unable to access 'https://github.com/GoogleCloudPlatform/gke-networking-api/': The requested URL returned error: 403 Error: Process completed with exit code 128.

We're specifying contents: write for dependabot's job:

• https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/controlling-permissions-for-github_token.

[google-oss-prow[bot]]

@billnapier: changing LGTM is restricted to collaborators

In response to [this](https://github.com/GoogleCloudPlatform/gke-networking-api/pull/31#pullrequestreview-2343200489): > Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes/test-infra](https://github.com/kubernetes/test-infra/issues/new?title=Prow%20issue:) repository.

[yswe]

/assign @bowei

[bowei]

/lgtm /approve

[google-oss-prow[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: billnapier, bowei, yswe

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/GoogleCloudPlatform/gke-networking-api/blob/main/OWNERS)~~ [bowei] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment