Update actions/download-artifact action to v7 (#88)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/integration_test.yaml

@@ -102,7 +102,7 @@ jobs:
           go install github.com/snapcore/spread/cmd/spread@latest
       - name: Download packed charm(s)
         timeout-minutes: 5
-        uses: actions/download-artifact@v6
+        uses: actions/download-artifact@v7
         with:
           pattern: ${{ inputs.artifact-prefix }}-*
           merge-multiple: true