test: add a performance test for PI with many tabs

Author: Watson1978

test/parse/test_processing_instruction.rb

@@ -116,5 +116,12 @@ def test_linear_performance_gt
         REXML::Document.new("<?xml version=\"1.0\" " + ">" * n + " ?>")
       end
     end
+
+    def test_linear_performance_tab
+      seq = [10000, 50000, 100000, 150000, 200000]
+      assert_linear_performance(seq, rehearsal: 10) do |n|
+        REXML::Document.new("<?name" + "\t" * n + "version=\"1.0\" > ?>")
+      end
+    end
   end
 end