build(deps): bump DeterminateSystems/flakehub-push from 3 to 4

Bumps [DeterminateSystems/flakehub-push](https://github.com/determinatesystems/flakehub-push) from 3 to 4.
- [Release notes](https://github.com/determinatesystems/flakehub-push/releases)
- [Commits](DeterminateSystems/flakehub-push@v3...v4)

---
updated-dependencies:
- dependency-name: DeterminateSystems/flakehub-push
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

.github/workflows/release.yml

@@ -30,7 +30,7 @@ jobs:
         with:
           ref: ${{ inputs.tag != null && format('refs/tags/{0}', inputs.tag) || '' }}
       - uses: DeterminateSystems/nix-installer-action@v9
-      - uses: DeterminateSystems/flakehub-push@v3
+      - uses: DeterminateSystems/flakehub-push@v4
         with:
           visibility: public
           tag: ${{ inputs.tag }}