Fix charts repo name in workflow call

When the test charts release workflow is triggered by scheduling, it
cannot rely on input parameters as if it were triggered manually.
Instead, the charts repo name must come from the environment, where it
is computed precisely based on how the workflow is triggered.

.github/workflows/release-against-test-charts.yml

@@ -176,6 +176,6 @@ jobs:
     needs: push-test-rancher-charts
     with:
       ref: ${{ github.ref }}
-      charts_repo: ${{github.event.inputs.charts_repo}}
+      charts_repo: ${{ env.charts_repo }}
       charts_branch: ${{ needs.push-test-rancher-charts.outputs.target_branch }}
       fleet_version: 999.9.9+up9.9.9