Build(deps): Bump actions/download-artifact from 4 to 6

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 4 to 6.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v4...v6)

---
updated-dependencies:
- dependency-name: actions/download-artifact
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/build-release.yml

@@ -129,7 +129,7 @@ jobs:
         fetch-depth: 0
 
     - name: Download artifacts
-      uses: actions/download-artifact@v4
+      uses: actions/download-artifact@v6
       with:
         name: nuget-package
         path: ./packages

.github/workflows/test-all-platforms.yml

@@ -79,7 +79,7 @@ jobs:
     if: always()
     steps:
       - name: Download all test result artifacts
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
         with:
           path: test-results