Fix pyright CI job (#11689)

Co-authored-by: Sebastian Rittau <srittau@rittau.biz>

.github/workflows/tests.yml

@@ -123,7 +123,9 @@ jobs:
           if [ -n "$DEPENDENCIES" ]; then
             source .venv/bin/activate
             echo "Installing packages: $DEPENDENCIES"
-            uv pip install $DEPENDENCIES
+            # https://github.com/python/typeshed/issues/11688
+            echo "Pillow<10.3" > constraints.txt
+            uv pip install -c constraints.txt $DEPENDENCIES
           fi
       - name: Activate the isolated venv for the rest of the job
         run: echo "$PWD/.venv/bin" >> $GITHUB_PATH