build: drop unused sanitize gem dev dependency

html-pipeline v3 uses Selma directly instead of the sanitize gem, and
nothing in this repo requires sanitize. The 'sanitize' method calls in
lib/github/markup/command_implementation.rb are an internal encoding
helper, not the gem.

Caught by Copilot's code review on #2061.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Signed-off-by: Zack Koppert <zkoppert@github.com>

Author: zkoppert

Gemfile.lock

@@ -35,7 +35,6 @@ GEM
     commonmarker (2.8.2-x86_64-linux)
     concurrent-ruby (1.3.6)
     connection_pool (3.0.2)
-    crass (1.0.6)
     creole (0.5.0)
     date (3.5.1)
     docile (1.4.1)
@@ -95,9 +94,6 @@ GEM
     rexml (3.4.4)
     rubypants (0.7.1)
     rugged (1.9.0)
-    sanitize (6.1.3)
-      crass (~> 1.0.2)
-      nokogiri (>= 1.12.0)
     securerandom (0.4.1)
     selma (0.5.0)
       rb_sys (~> 0.9)
@@ -157,7 +153,6 @@ DEPENDENCIES
   rdoc (~> 7.2.0)
   redcarpet
   rexml
-  sanitize (>= 4.6.3)
   simplecov (~> 0.22)
   twitter-text (~> 1.14)
   wikicloth (= 0.8.3)

github-markup.gemspec

@@ -27,7 +27,6 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'activesupport', '~> 8.1.3'
   s.add_development_dependency 'minitest', '>= 5.4.3', '~> 6.0'
   s.add_development_dependency 'html-pipeline', '~> 3.2'
-  s.add_development_dependency 'sanitize', '>= 4.6.3'
   s.add_development_dependency 'nokogiri', '~> 1.19.2'
   s.add_development_dependency 'nokogiri-diff', '~> 0.3.0'
   s.add_development_dependency "github-linguist", ">= 7.1.3"