Skip tainted examples for stringio

spec/ruby/library/stringio/append_spec.rb

@@ -29,10 +29,12 @@ describe "StringIO#<< when passed [Object]" do
     @io.string.should == "example\000\000\000\000\000\000\000\000just testing"
   end
 
+  ruby_version_is ""..."2.7"
     it "taints self's String when the passed argument is tainted" do
       (@io << "test".taint)
       @io.string.tainted?.should be_true
     end
+  end
 
   it "does not taint self when the passed argument is tainted" do
     (@io << "test".taint)

spec/ruby/library/stringio/reopen_spec.rb

@@ -202,10 +202,12 @@ describe "StringIO#reopen when passed [Object]" do
   end
 
   # NOTE: WEIRD!
+  ruby_version_is ""..."2.7"
     it "taints self when the passed Object was tainted" do
       @io.reopen(StringIO.new("reopened").taint)
       @io.tainted?.should be_true
     end
+  end
 end
 
 describe "StringIO#reopen when passed no arguments" do
@@ -270,12 +272,14 @@ describe "StringIO#reopen" do
     str.should == ''
   end
 
+  ruby_version_is ""..."2.7"
     it "taints self if the provided StringIO argument is tainted" do
       new_io = StringIO.new("tainted")
       new_io.taint
       @io.reopen(new_io)
       @io.tainted?.should == true
     end
+  end
 
   it "does not truncate the content even when the StringIO argument is in the truncate mode" do
     orig_io = StringIO.new("Original StringIO", IO::RDWR|IO::TRUNC)

spec/ruby/library/stringio/shared/write.rb

@@ -45,10 +45,12 @@ describe :stringio_write_string, shared: true do
     @io.pos.should eql(4)
   end
 
+  ruby_version_is ""..."2.7"
     it "taints self's String when the passed argument is tainted" do
       @io.send(@method, "test".taint)
       @io.string.tainted?.should be_true
     end
+  end
 
   it "does not taint self when the passed argument is tainted" do
     @io.send(@method, "test".taint)