Bump actions/download-artifact from 5 to 6

Bumps [actions/download-artifact](https://github.com/actions/download-artifact) from 5 to 6.
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v5...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] <[email protected]>

Author: dependabot[bot]

.github/workflows/prepare-release.yml

@@ -148,7 +148,7 @@ jobs:
 
       # when no artifact is specified, all artifacts are downloaded and expanded into CWD
       - name: Fetch executables
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
 
       # example: linux_amd64/ -> temporal-test-server_1.2.3_linux_amd64
       # the name of the directory created becomes the basename of the archive (*.tar.gz or *.zip) and