[torchx][CI] Upgrade pip prior to installing deps for python-unittests

Author: Kiuk Chung

.github/workflows/python-unittests.yaml

@@ -28,6 +28,11 @@ jobs:
           architecture: x64
       - name: Checkout TorchX
         uses: actions/checkout@v2
+      - name: Upgrade pip
+        run: |
+	  set -eux
+	  python -m pip install --upgrade pip
+	  pip --version
       - name: Install dependencies
         run: |
           set -eux