ci: pip install -U transformers to override wheel's <5 constraint

The continuous-release wheel is built from main which still has
transformers<5 in its metadata. pip install without -U sees 4.57.6
already satisfied and won't upgrade to v5.x. Adding -U forces the
upgrade past the baked-in constraint.

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

Author: Titus-von-Koeller

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

@@ -65,7 +65,7 @@ jobs:
 
       - name: Install transformers and clone matching tag
         run: |
-          pip install transformers accelerate
+          pip install -U transformers accelerate
           TRANSFORMERS_VERSION=$(pip show transformers | awk '/^Version:/ {print $2}')
           echo "Installed transformers v${TRANSFORMERS_VERSION}"
           git clone --depth=1 --branch "v${TRANSFORMERS_VERSION}" \
@@ -120,7 +120,7 @@ jobs:
 
       - name: Install transformers and clone matching tag
         run: |
-          pip install transformers accelerate
+          pip install -U transformers accelerate
           TRANSFORMERS_VERSION=$(pip show transformers | awk '/^Version:/ {print $2}')
           echo "Installed transformers v${TRANSFORMERS_VERSION}"
           git clone --depth=1 --branch "v${TRANSFORMERS_VERSION}" \