Bump dawidd6/action-download-artifact from 20 to 21

Bumps [dawidd6/action-download-artifact](https://github.com/dawidd6/action-download-artifact) from 20 to 21.
- [Release notes](https://github.com/dawidd6/action-download-artifact/releases)
- [Commits](dawidd6/action-download-artifact@v20...v21)

---
updated-dependencies:
- dependency-name: dawidd6/action-download-artifact
  dependency-version: '21'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/documentation-push.yml

@@ -35,15 +35,15 @@ jobs:
     - uses: actions/checkout@v6
 
     - name: Download Documentation Artifacts
-      uses: dawidd6/action-download-artifact@v20
+      uses: dawidd6/action-download-artifact@v21
       with:
         workflow: documentation-build.yml
         commit: ${{ github.event.workflow_run.head_sha || github.sha }}
         name: documentation-artifacts
         path: /__w/hpx/hpx/build/share/hpx/docs
 
     - name: Download Depreport Artifacts
-      uses: dawidd6/action-download-artifact@v20
+      uses: dawidd6/action-download-artifact@v21
       with:
         workflow: depreport.yml
         commit: ${{ github.event.workflow_run.head_sha || github.sha }}