add inspect to Requirement subclass

Closes Homebrew/homebrew#37116.

Signed-off-by: Xu Cheng <xucheng@me.com>

Library/Homebrew/requirements.rb

@@ -43,6 +43,10 @@ class XcodeDependency < Requirement
       EOS
     end
   end
+
+  def inspect
+    "#<#{self.class.name}: #{name.inspect} #{tags.inspect} version=#{@version.inspect}>"
+  end
 end
 
 class MysqlDependency < Requirement

Library/Homebrew/requirements/mpi_dependency.rb

@@ -34,6 +34,10 @@ class MPIDependency < Requirement
     quiet_system compiler, '--version'
   end
 
+  def inspect
+    "#<#{self.class.name}: #{name.inspect} #{tags.inspect} lang_list=#{@lang_list.inspect}>"
+  end
+
   satisfy do
     @lang_list.each do |lang|
       case lang