Auto approve and merge dependabot pull requests. Credit to Phillip Verheyden.

autoapprove-dependabot.yml

name: Dependabot auto-approve
on: pull_request_target
permissions:
  pull-requests: write

# From the docs at https://github.com/dependabot/fetch-metadata#enabling-auto-merge
jobs:
  dependabot:
    runs-on: ubuntu-latest
    if: ${{ github.event.pull_request.user.login == 'dependabot[bot]' }}
    steps:
      - name: Dependabot metadata
        id: metadata
        uses: dependabot/fetch-metadata@v1.3.0
        with:
          github-token: "${{ secrets.GITHUB_TOKEN }}"
      - name: Auto-approve minor or patch updates
        if: |
          steps.metadata.outputs.update-type == 'version-update:semver-minor'
                || steps.metadata.outputs.update-type == 'version-update:semver-patch'
        run: gh pr review --approve "$PR_URL"
        env:
          PR_URL: ${{github.event.pull_request.html_url}}
          GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}

automerge-dependabot.yml

name: Dependabot auto-merge
on: pull_request
permissions:
  pull-requests: write
  contents: write

# Mostly from https://docs.github.com/en/code-security/supply-chain-security/keeping-your-dependencies-updated-automatically/automating-dependabot-with-github-actions#enable-auto-merge-on-a-pull-request

jobs:
  dependabot:
    runs-on: ubuntu-latest
    if: ${{ github.event.pull_request.user.login == 'dependabot[bot]' }}
    steps:
      - name: Dependabot metadata
        id: metadata
        uses: dependabot/fetch-metadata@v1.3.0
        with:
          github-token: "${{ secrets.GITHUB_TOKEN }}"
      - name: Enable auto-merge for Dependabot PRs
        run: gh pr merge --auto --squash "$PR_URL"
        env:
          PR_URL: ${{github.event.pull_request.html_url}}
          GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}

In automerge-dependabot.yml the --squash argument is not necessary