[DRE-maint] ruby-graphviz is marked for autoremoval from testing

[Debian testing autoremoval watch]

ruby-graphviz 1.2.3-1 is marked for autoremoval from testing on 2020-03-23

It is affected by these RC bugs:
952039: ruby-graphviz: FTBFS: ERROR: Test "ruby2.7" failed: /<<PKGBUILDDIR>>/test/output/dot/hello_test.rb:18:in `<top (required)>': undefined method `graph' for nil:NilClass (NoMethodError)