Disable coverage for impossible cases

repo_management/operations.py:
Do not try to cover the cases, that coveragepy is not able to cover
(e.g. async for loops with awaitables).
Upstream coveragepy seems to still have issues coverying different kinds
of concurrency techniques:
https://github.com/nedbat/coveragepy/issues/1012
3 jobs for issues/15 in 3 minutes and 27 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Test
passed #19664
coverage

00:00:45

passed #19665
integration

00:03:26

passed #19663
linter

00:00:33