add a summary report flag for run_examples on CI (#6035)
Currently, it's hard to derive which example tests were run on CI, and which weren't. Adding `-rA` flag to `pytest`, will now include a summary like:
```
==================================================================== short test summary info =====================================================================
PASSED examples/test_examples.py::ExamplesTests::test_generation
PASSED examples/test_examples.py::ExamplesTests::test_run_glue
PASSED examples/test_examples.py::ExamplesTests::test_run_language_modeling
PASSED examples/test_examples.py::ExamplesTests::test_run_squad
FAILED examples/test_examples.py::ExamplesTests::test_run_pl_glue - AttributeError: 'Namespace' object has no attribute 'gpus'
============================================================ 1 failed, 4 passed, 8 warnings in 42.96s ============================================================
```
which makes it easier to validate whether some example is being covered by CI or not.
