update python command for mi250 (#652)

Author: saienduri

.github/workflows/test_models.yml

@@ -36,9 +36,9 @@ jobs:
       - name: Sync source deps
         # build IREE from source with -DIREE_BUILD_TRACY=ON if getting tracy profile
         run: |
-          python -m venv turbine_venv
+          python3.11 -m venv turbine_venv
           source turbine_venv/bin/activate
-          python -m pip install --upgrade pip
+          python3.11 -m pip install --upgrade pip
           # Note: We install in three steps in order to satisfy requirements
           # from non default locations first. Installing the PyTorch CPU
           # wheels saves multiple minutes and a lot of bandwidth on runner setup.