add a changelog lint job to CI

[briantist]

SUMMARY

We should run antsibull-changelog lint to ensure that fragments are formatted correctly.

ISSUE TYPE

• Feature Idea

[briantist]

hm, I forgot that sanity tests check this, is there something the lint command might catch that sanity wouldn't? @felixfontein

[felixfontein]

@briantist ansible-test sanity simply runs antsibull-changelog lint.

[briantist]

perfect, sounds like I don't need a separate job for this after all