ci: temporarily disable multi-GPU jobs until runner is provisioned

The bandb-aws-g6-12xlarge-plus runner doesn't exist yet. Queued jobs
with no runner hang indefinitely, blocking the report job (which needs
all jobs to complete). Set `if: false` on both multi-GPU jobs so the
single-GPU tests and Slack reporting can run while infra provisions the
multi-GPU runner.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Titus-von-Koeller

.github/workflows/tests-integration-nightly.yml

@@ -100,7 +100,7 @@ jobs:
 
   test-transformers-multigpu:
     name: Transformers bnb tests (multi GPU)
-    if: github.repository == 'bitsandbytes-foundation/bitsandbytes'
+    if: false  # disabled until bandb-aws-g6-12xlarge-plus runner is provisioned
     runs-on: bandb-aws-g6-12xlarge-plus-use1-public-80  # 4× L4 (2 used)
     steps:
       - name: Show GPU information
@@ -270,7 +270,7 @@ jobs:
 
   test-peft-multigpu:
     name: PEFT bnb tests (multi GPU)
-    if: github.repository == 'bitsandbytes-foundation/bitsandbytes'
+    if: false  # disabled until bandb-aws-g6-12xlarge-plus runner is provisioned
     runs-on: bandb-aws-g6-12xlarge-plus-use1-public-80  # 4× L4
     steps:
       - name: Show GPU information