[DRE-maint] Bug#893823: ruby-minitest-shared-description FTBFS with Ruby 2.5

[Adrian Bunk]

Source: ruby-minitest-shared-description
Version: 1.0.0-1
Severity: serious
Tags: buster sid

https://tests.reproducible-builds.org/debian/rb-pkg/unstable/amd64/ruby-minitest-shared-description.html

...
┌──────────────────────────────────────────────────────────────────────────────┐
│ Run tests for ruby2.5 from debian/ruby-tests.rb                              │
└──────────────────────────────────────────────────────────────────────────────┘

RUBYLIB=/build/1st/ruby-minitest-shared-description-1.0.0/debian/ruby-minitest-shared-description/usr/lib/ruby/vendor_ruby:. GEM_PATH=debian/ruby-minitest-shared-description/usr/share/rubygems-integration/all:/var/lib/gems/2.5.0:/usr/lib/x86_64-linux-gnu/rubygems-integration/2.5.0:/usr/share/rubygems-integration/2.5.0:/usr/share/rubygems-integration/all ruby2.5 debian/ruby-tests.rb
/usr/bin/ruby2.5 -I lib -rubygems ./spec/minitest-shared_description_spec.rb
/usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require': cannot load such file -- ubygems (LoadError)
	from /usr/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
rake aborted!
Command failed with status (1): [/usr/bin/ruby2.5 -I lib -rubygems ./spec/m...]
/build/1st/ruby-minitest-shared-description-1.0.0/Rakefile:15:in `block in <top (required)>'
Tasks: TOP => spec
(See full trace by running task with --trace)
ERROR: Test "ruby2.5" failed. Exiting.
dh_auto_install: dh_ruby --install /build/1st/ruby-minitest-shared-description-1.0.0/debian/ruby-minitest-shared-description returned exit code 1
make: *** [debian/rules:6: binary] Error 1