Bump actions/download-artifact from 7 to 8

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 7 to 8.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v7...v8)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: '8'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/build-test.yml

@@ -102,7 +102,7 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v6
       - name: Download app artifact
-        uses: actions/download-artifact@v7
+        uses: actions/download-artifact@v8
         with:
           name: app-${{ env.OPENFOAM }}-${{ runner.arch }}
           path: build

.github/workflows/release.yml

@@ -27,7 +27,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Download app artifacts
-        uses: actions/download-artifact@v7
+        uses: actions/download-artifact@v8
         with:
           pattern: app-*
           merge-multiple: true