Syntactic sugar for marking tests to be
skipped in a particular mode.
There is skip_in_debug/skip_in_release in suite.yaml,
but they can be applied only on the entire file,
which is unnatural and inconvenient. Also, they
don't allow to specify a reason why the test is skipped.
Separate dictionary skipped_funcs is needed since
we can't use pytest fixtures in decorators.