fix: barretenberg-nightly-debug.yml

Author: ludamad

.github/workflows/barretenberg-nightly-debug-build.yml

@@ -16,7 +16,7 @@ jobs:
       - name: Checkout
         uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
         with:
-          ref: main
+          ref: next
 
       - name: Run debug build
         timeout-minutes: 120