...
- name: print puma version
  command: puma -V
  register: puma_v

- name: print output
  debug:
    var: puma_v

- name: gem install puma -v 3.12.0
  gem:
    name: puma
    version: 3.12.0
    state: present
    force: true
  when: puma_v.stdout != 'puma version 3.12.0'

...