chore(deps): bump actions/upload-artifact from 3 to 4

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 3 to 4.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](https://github.com/actions/upload-artifact/compare/v3...v4)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/check-docs.yml

@@ -40,7 +40,7 @@ jobs:
         run: nix build .#${{ matrix.package }} --print-build-logs
 
       - name: Upload doc artifacts
-        uses: actions/upload-artifact@v3
+        uses: actions/upload-artifact@v4
         with:
           name: doc
           path: result/share/doc/neovim-flake/