Warning but not quit after URL check

@jnavila

It seems that url check only output warnings, but not quit

HTML-Proofer found 8 failures!
Command failed with status (1): [htmlproofer progit.html]
Error when checking books (ignored)

Could you help us to just ignore this check? @jnavila
Maybe it could be like this:
Fix htmlproofer invocation · progit/progit2@8de1de7

I submitted a PR #520 to solve the building failure problem.
Here is how I resolved it:

First,from the building log progit2-zh/actions/runs/10380612436/job/28740723111, I found that Gemfile from https://raw.githubusercontent.com/progit/progit2-pub/master/Gemfile.new, and Rakefile from https://raw.githubusercontent.com/progit/progit2-pub/master/Rakefile.
I tried to use these two files, build locally, but it does not work. The ones that confused me are ENV['GITHUB_REPOSITORY'] and `ENV['TRAVIS_REPO_SLUG']'. I do not know where they are defined.
So why not just use the Gemfile and Rakefile files from the progit2 repository? So after a series of revisions, I made it.

Things to be attentive:

Ruby version: 2.7.8, It is same with the version shown in the log /opt/hostedtoolcache/Ruby/2.7.8/x64/bin.
The asciidoctor-pdf-cjk-kai_gen_gothic code was outdated and no longer accepted any PR, so I modified it and replaced it with my fork project address warning: calling URI.open via Kernel#open is deprecated chloerei/asciidoctor-pdf-cjk-kai_gen_gothic#16.
I noticed the kendlegen download from this https://web.archive.org/web/20150803131026/https://kindlegen.s3.amazonaws.com/kindlegen_linux_2.6_i3 86_v2_9.tar.gz, I couldn't download kindlegen due to some network problems, so I didn't add buid_mobi when I built it locally. But I added mobi support to the code I submitted.
This file (.github/workflows/pr-build.yml) had adjusted to get the new Gemfile and Rakefile.
Modified the configuration file (.github/workflows/release-on-merge.yml) to adapt to the new build process.

现在应该可以build和release成功了，晚上又不小心改动了字体库那边文件的名字，给它恢复并存档了，以后没问题的话，我就不动它了。