ci: bump akhileshns/heroku-deploy from 3.14.15 to 4 (#25)

Bumps [akhileshns/heroku-deploy](https://github.com/akhileshns/heroku-deploy) from 3.14.15 to 4.
- [Release notes](https://github.com/akhileshns/heroku-deploy/releases)
- [Commits](AkhileshNS/heroku-deploy@v3.14.15...v4)

---
updated-dependencies:
- dependency-name: akhileshns/heroku-deploy
  dependency-version: '4'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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Author: dependabot[bot]

.github/workflows/deploy.yml

@@ -18,7 +18,7 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Deploy to Heroku
-        uses: akhileshns/heroku-deploy@v3.14.15
+        uses: akhileshns/heroku-deploy@v4
         with:
           heroku_api_key: ${{ secrets.HEROKU_API_KEY }}
           heroku_app_name: reitz-wishlist