Basic test for .gemspec sanity

[ahukkanen]

🎩 What? Why?

Since I recently noticed some cross dependency issues with the Decidim gem, I added this test to check that the .gemspec files do not define the decidim root gem as their dependency.

This might not fix the whole problem with the individual gems (see #13062) but it's a start to making sure that gems could work without requiring all the other gems as their dependencies.

📌 Related Issues

• Related to Loosen the dependencies on the decidim-dev gem #13052

Testing

• Wait for Loosen the dependencies on the decidim-dev gem #13052 to be merged
• After merged, wait for this branch to be updated with the latest changes
• After updated, see that CI is green

[andreslucena]

I applied the decidim-dev.gemspec as it was before #13052, and have this:

$ bundle exec rspec spec/gemspecs_spec.rb
.F

Failures:

  1) Gemspec sanity decidim-dev spec does not require the `decidim` gem
     Failure/Error: expect(decidim_dev_spec).to be_decidim_clean
       expected 'decidim-dev' gem not to have the 'decidim' gem as its dependency
     # ./spec/gemspecs_spec.rb:21:in `block (3 levels) in <top (required)>'

Finished in 0.05099 seconds (files took 0.06076 seconds to load)
2 examples, 1 failure

Failed examples:

rspec ./spec/gemspecs_spec.rb:20 # Gemspec sanity decidim-dev spec does not require the `decidim` gem

So, it works as expected. Thanks for the PR!