Add back standalone task azure CI step (#14366)

Author: carmocca

.azure/gpu-tests.yml

@@ -120,6 +120,15 @@ jobs:
       timeoutInMinutes: "35"
       condition: eq(variables['continue'], '1')
 
+    - bash: bash run_standalone_tasks.sh
+      workingDirectory: tests/tests_pytorch
+      env:
+        PL_USE_MOCKED_MNIST: "1"
+        PL_RUN_CUDA_TESTS: "1"
+      displayName: 'Testing: PyTorch standalone tasks'
+      timeoutInMinutes: "10"
+      condition: eq(variables['continue'], '1')
+
     - bash: |
         python -m coverage report
         python -m coverage xml