Bump peter-evans/create-pull-request from 3 to 4

Bumps [peter-evans/create-pull-request](https://github.com/peter-evans/create-pull-request) from 3 to 4.
- [Release notes](https://github.com/peter-evans/create-pull-request/releases)
- [Commits](https://github.com/peter-evans/create-pull-request/compare/v3...v4)

---
updated-dependencies:
- dependency-name: peter-evans/create-pull-request
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/nix-flake-update.yml

@@ -18,7 +18,7 @@ jobs:
         run: nix flake update
       - name: Create Pull Request
         id: cpr
-        uses: peter-evans/create-pull-request@v3
+        uses: peter-evans/create-pull-request@v4
         with:
           commit-message: Update flakes
           committer: GitHub <noreply@github.com>