[3.14] pythongh-133982: Update test_bufio to use self.open (pythongh-133983) (pythongh-134428)

(cherry picked from commit 84d5f8d)

Co-authored-by: Cody Maloney <[email protected]>

Author: miss-islington

Lib/test/test_bufio.py

@@ -28,7 +28,7 @@ def try_one(self, s):
             f.write(b"\n")
             f.write(s)
             f.close()
-            f = open(os_helper.TESTFN, "rb")
+            f = self.open(os_helper.TESTFN, "rb")
             line = f.readline()
             self.assertEqual(line, s + b"\n")
             line = f.readline()