Make the `spec/fixtures/*/Gemfile.lock` files programmaticaly generated

[postmodern]

Auto-generate the Gemfile.lock files used in the specs. This will avoid dealing with dependabot alerts. The Gemfile.lock should be much simpler and only with a few gems.

[JuanVqz]

hey @postmodern! What do you think the best way is to fix this issue?