ci: run git pull before committing pytorch version updates (llvm#1716)

The RollPyTorch action often takes more than 1.5 hours to finish.
During this time, if another PR is merged, then the RollPyTorch action
needs to first pull the merged changes before committing the updates to
the PyTorch commit hash and version files.  This patch adds the required
`git pull` statement, without which, the subsequent `git push` statement
fails, causing the RollPyTorch action to fail as well.

.github/workflows/RollPyTorch.yml

@@ -79,6 +79,7 @@ jobs:
         git config user.name "Roll PyTorch Action"
         git fetch --recurse-submodules=no
         git checkout main
+        git pull origin main
         git add pytorch-hash.txt pytorch-requirements.txt lib/Dialect/Torch/Transforms/AbstractInterpLibrary.cpp include/torch-mlir/Dialect/Torch/IR/GeneratedTorchOps.td
         git diff --cached --exit-code || (git commit -m "update PyTorch version to ${{ env.PT_RELEASE }}" && git push --set-upstream origin main)