Add paragraphs to test_dependencies in .info.yml

Problem/Motivation

In #2902164-53: Controlled-by fields inside a Paragraph don't work, @josephleon and myself are adding support for paragraphs in conditional_fields. We are taking a test-driven approach, i.e.: write the test first, then fix the issue.

In order for us to test this, we need both conditional_fields and paragraphs installed when we run tests, but we don't want to make conditional_fields depend on paragraphs for regular users.

Drupal.org allows you to handle the case where you want a module installed during testbot tests, but not require the module for regular users, i.e.: so you can test integration between two modules, by adding a test_dependencies section to your module's .info.yml file.

However, there's a big limitation - adding a test_dependencies section in the same patch that you add tests that use that dependency is not allowed - the test_dependencies section must already be in the branch before you can write tests that use the dependency, and a new -dev release must have already been rolled out for changes in the branch (once every 24 hours). For more information, see the following documentation:

1. "test_dependencies" point in "Complete example" section of "Let Drupal know about your module with an .info.yml file"
2. "Dependencies for tests" in Managing dependencies for a contributed project"
3. "Tests pass locally but fail when run by drupal.org's testbot" section of "Running PHPUnit tests"

Proposed resolution

Add...

test_dependencies:
  - paragraphs:paragraphs

... to conditional_fields.info.yml.

Remaining tasks

1. Write a patch
2. Review and feedback
3. RTBC and feedback
4. Commit
5. (Wait for dev release to happen?)

User interface changes

None.

API changes

None.

Data model changes

None.