CI Activate single core multi backend bnb tests (huggingface#2008)

See huggingface#1866 for context.

Let's check if this issue has resolved itself by now.

.github/workflows/nightly-bnb.yml

@@ -66,22 +66,21 @@ jobs:
           status: ${{ steps.import.outcome }}
           slack_token: ${{ secrets.SLACK_CIFEEDBACK_BOT_TOKEN }}
 
-      # TODO: uncomment this block if error is solved or bnb multi backend branch is merged
-      # - name: Run examples on single GPU
-      #   id: examples_tests
-      #   if: always()
-      #   run: |
-      #     source activate peft
-      #     make tests_examples_single_gpu_bnb
-
-      # - name: Post to Slack
-      #   if: always()
-      #   uses: huggingface/hf-workflows/.github/actions/post-slack@main
-      #   with:
-      #     slack_channel: ${{ secrets.BNB_SLACK_CHANNEL_ID }}
-      #     title: 🤗 Results of bitsandbytes examples tests - single GPU
-      #     status: ${{ steps.examples_tests.outcome }}
-      #     slack_token: ${{ secrets.SLACK_CIFEEDBACK_BOT_TOKEN }}
+      - name: Run examples on single GPU
+        id: examples_tests
+        if: always()
+        run: |
+          source activate peft
+          make tests_examples_single_gpu_bnb
+
+      - name: Post to Slack
+        if: always()
+        uses: huggingface/hf-workflows/.github/actions/post-slack@main
+        with:
+          slack_channel: ${{ secrets.BNB_SLACK_CHANNEL_ID }}
+          title: 🤗 Results of bitsandbytes examples tests - single GPU
+          status: ${{ steps.examples_tests.outcome }}
+          slack_token: ${{ secrets.SLACK_CIFEEDBACK_BOT_TOKEN }}
 
       - name: Run core tests on single GPU
         id: core_tests