Disable regression tests temporarily

[srittau]

They fail intermittently, see #11220 for details.

[AlexWaygood]

my worry is that the intermittent test failure indicates some kind of import cycle between the os and resource modules that may cause mypy to crash in "real life" outside of our test suite. But it is odd that it only seems to be happening with regr_test.py, and not with mypy_test.py.

I also worry that these tests will quickly start to fail with mypy if we do this.

[AlexWaygood]

If we need a stopgap to fix the intermittent failures, I'd honestly prefer to revert 3edfd90. All the failures mention "Cannot find module for resource.struct_rusage", and the test failures started immediately after that commit, so I think it must be the cause (although I cannot explain it -- though I haven't done any in-depth investigation yet).

[Avasam]

I have no idea either. But I'm down to revert it if investigation requires much more time.