Fix failing slsa GH action

The 2.0 release also upgraded the artifact uploader/downloader, which is what broke our workflow.

See https://github.com/slsa-framework/slsa-github-generator/blob/v2.0.0/CHANGELOG.md#v200-breaking-change-upload-artifact-and-download-artifact

Change-Id: Ia17d1cbf358aebbb0ea7f5e97a24f2220b784431

.github/workflows/reusable_provenance.yaml

@@ -126,13 +126,13 @@ jobs:
           EOF
 
       - name: Download the built artifact
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: ${{ needs.generate_provenance.outputs.build-outputs-name }}
           path: downloads
 
       - name: Download the DSSE document
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name:
             ${{ needs.generate_provenance.outputs.attestations-download-name }}
@@ -179,13 +179,13 @@ jobs:
 
     steps:
       - name: Download the built artifact
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name: ${{ needs.generate_provenance.outputs.build-outputs-name }}
           path: downloads
 
       - name: Download the DSSE document
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
           name:
             ${{ needs.generate_provenance.outputs.attestations-download-name }}