Run check_contrib() once, declare as dependency of html/pdf/epub/mobi #1663
Description
The process could be improved by only running check_contrib() once (by declaring it a dependency of html/pdf/epub/mobi). But it is out of scope of this PR.
Originally posted by @slonopotamus in #1656 (comment)
Link to rake file we need to change: https://github.com/progit/progit2/blob/main/Rakefile