Strictly source_code_uri for rubygems.org

Author: sue445

_gem/go_gem.gemspec

@@ -15,7 +15,7 @@ Gem::Specification.new do |spec|
   spec.required_ruby_version = ">= 3.3.0"
 
   spec.metadata["homepage_uri"] = spec.homepage
-  spec.metadata["source_code_uri"] = spec.homepage
+  spec.metadata["source_code_uri"] = "#{spec.homepage}/tree/main/_gem"
   spec.metadata["changelog_uri"] = "#{spec.homepage}/blob/main/CHANGELOG.md"
   spec.metadata["documentation_uri"] = "https://ruby-go-gem.github.io/go-gem-wrapper/"
   spec.metadata["rubygems_mfa_required"] = "true"