Skip a broken RDoc test

http://ci.rvm.jp/results/trunk-yjit@phosphorus-docker/4309535
http://ci.rvm.jp/results/trunk-random0@phosphorus-docker/4309536
http://ci.rvm.jp/results/trunk-random1@phosphorus-docker/4309538
http://ci.rvm.jp/results/trunk-random2@phosphorus-docker/4309541
http://ci.rvm.jp/results/trunk-random3@phosphorus-docker/4309544
http://ci.rvm.jp/results/trunk-no-mjit@phosphorus-docker/4309550
http://ci.rvm.jp/results/trunk-yjit@phosphorus-docker/4309556
http://ci.rvm.jp/results/trunk-random0@phosphorus-docker/4309562
http://ci.rvm.jp/results/trunk-random1@phosphorus-docker/4309564
http://ci.rvm.jp/results/trunk-random2@phosphorus-docker/4309567
http://ci.rvm.jp/results/trunk-random3@phosphorus-docker/4309570
http://rubyci.s3.amazonaws.com/solaris10-gcc/ruby-master/log/20221127T200003Z.fail.html.gz
http://ci.rvm.jp/results/trunk-random-repeat@phosphorus-docker/4309581
http://rubyci.s3.amazonaws.com/freebsd12/ruby-master/log/20221127T203002Z.fail.html.gz
http://ci.rvm.jp/results/trunk-yjit@phosphorus-docker/4309588

Author: k0kubun

test/rdoc/test_rdoc_generator_darkfish.rb

@@ -113,6 +113,7 @@ def test_generate
     refute_match(/Ignored/, File.read('index.html'))
     summary = File.read('index.html')[%r[<summary.*Klass\.html.*</summary>.*</details>]m]
     assert_match(%r[Klass/Inner\.html".*>Inner<], summary)
+    omit 'The following line crashes with "invalid byte sequence in US-ASCII" on ci.rvm.jp and some RubyCIs'
     klassnav = File.read('Klass.html')[%r[<div class="nav-section">.*<div id="class-metadata">]m]
     assert_match(
       %r[<li>\s*<details open>\s*<summary>\s*<a href=\S+>Heading 1</a>\s*</summary>\s*<ul]m,