[DRE-maint] Bug#978975: ruby-em-redis FTBFS on IPV6-only buildds

[Adrian Bunk]

Source: ruby-em-redis
Version: 0.3.0+gh-2
Severity: serious
Tags: ftbfs

https://buildd.debian.org/status/fetch.php?pkg=ruby-em-redis&arch=all&ver=0.3.0%2Bgh-2.1&stamp=1609255928&raw=0

...
EventMachine::ConnectionError: unable to resolve address: Address family for hostname not supported
	/usr/lib/ruby/vendor_ruby/eventmachine.rb:679:in `connect_server': EventMachine::Protocols::Redis - should be able to provide a logger
	/usr/lib/ruby/vendor_ruby/eventmachine.rb:679:in `bind_connect'
	/usr/lib/ruby/vendor_ruby/eventmachine.rb:655:in `connect'
	/<<PKGBUILDDIR>>/lib/em-redis/redis_protocol.rb:321:in `connect'
	/<<PKGBUILDDIR>>/spec/redis_commands_spec.rb:9:in `block (2 levels) in <top (required)>'
	/<<PKGBUILDDIR>>/spec/redis_commands_spec.rb:16:in `block in <top (required)>'
...
90 specifications (32 requirements), 0 failures, 75 errors
ERROR: Test "ruby2.7" failed. Exiting.
dh_auto_install: error: dh_ruby --install /<<BUILDDIR>>/ruby-em-redis-0.3.0\+gh/debian/ruby-em-redis returned exit code 1
make[1]: *** [debian/rules:26: override_dh_auto_install] Error 25