[RELEASE-ONLY CHANGES for 2.3] cherry-pick ea437b3 to fix windows CI (#3769)

Unpin mkl version and install pybind11 to get the windows CI working again

This fixes #3767

Author: ahmadsharif1

.github/scripts/unittest-windows/install.sh

@@ -29,8 +29,7 @@ else
     cudatoolkit="pytorch-cuda=${version}"
 fi
 printf "Installing PyTorch with %s\n" "${cudatoolkit}"
-conda install -y -c "pytorch-${UPLOAD_CHANNEL}" -c nvidia pytorch "${cudatoolkit}"  pytest
-conda install -y -c conda-forge mkl=2020.4
+conda install -y -c "pytorch-${UPLOAD_CHANNEL}" -c nvidia pytorch "${cudatoolkit}"  pytest pybind11
 
 torch_cuda=$(python -c "import torch; print(torch.cuda.is_available())")
 echo torch.cuda.is_available is $torch_cuda