Bump actions/download-artifact from 4 to 8 (#881)

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 4 to 8.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v4...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>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/prep_release.yml

@@ -98,7 +98,7 @@ jobs:
 
     steps:
     - name: Download JAR
-      uses: actions/download-artifact@v4
+      uses: actions/download-artifact@v8
       with:
         name: fat-jar
 
@@ -137,14 +137,14 @@ jobs:
 
     steps:
     - name: Download release assets
-      uses: actions/download-artifact@v4
+      uses: actions/download-artifact@v8
       with:
         name: release-assets
         path: release-assets
         merge-multiple: true
 
     - name: Download native binaries
-      uses: actions/download-artifact@v4
+      uses: actions/download-artifact@v8
       with:
         pattern: viash-*
         path: native-binaries