test: disable app-luatest/fiber_parent_backtrace_test.lua on macOS/M1

Regular testing routine on macOS/M1 platforms will be enabled back in
the last patch of the series, but there are some failures unrelated to
the changes made within the previous commits. Hence it was decided to
add the skip_if directive to app-luatest/fiber_parent_backtrace_test.lua
for now.

Relates to tarantool/tarantool-qa#309

NO_DOC=tests
NO_CHANGELOG=tests