build(deps): bump DeterminateSystems/flakehub-push from 4 to 5

Bumps [DeterminateSystems/flakehub-push](https://github.com/determinatesystems/flakehub-push) from 4 to 5.
- [Release notes](https://github.com/determinatesystems/flakehub-push/releases)
- [Commits](DeterminateSystems/flakehub-push@v4...v5)

---
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/monthly.yml

@@ -28,7 +28,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: DeterminateSystems/nix-installer-action@v14
-      - uses: DeterminateSystems/flakehub-push@v4
+      - uses: DeterminateSystems/flakehub-push@v5
         with:
           visibility: public
           rolling: true