Added pytest.mark.xfail on test_distrib_gloo_cpu_or_gpu()

[nishantb06]

Fixes #2453

Description:
After correcting the syntax of pytest.approx(), Assertion error was detected due to the values not being the same. Which is why pytest.mark.xfail was added on test_distrib_gloo_cpu_or_gpu()

Check list:

• New tests are added (if a new feature is added)
• New doc strings: description and/or example code are in RST format
• Documentation is updated (if required)

[vfdev-5]

@nishantb06 thanks for the PR, let's xfail all tests in this python file.
xla and hvd tests are also failing: https://github.com/pytorch/ignite/runs/5094361286?check_suite_focus=true#step:9:483

• test_distrib_hvd
• test_distrib_xla_nprocs
• test_distrib_nccl_gpu

[vfdev-5]

@nishantb06 thanks for the update, I added manually 2 more xfails to disable all the tests and also restart CI. Let's see if it passes now and we can merge this PR.

[nishantb06]

Thank you.