Copied the examples from the bug report and added an additional test case with the failing behavior multiple times in the same expression.

Black always uses double quotes. Test would also fail on this, but that's not the reason the test is failing to begin with.

Correct output was missing a parentheses group in the original.

Fix `omit` generator exiting early after seeing two consecutive non-empty bracket pairs before seeing a magic comma. This does cause a regression with `trailing_comma_optional_parens2` and it still does not fix lines with multiple magic commas.