bpo-40286: Use random.randbytes() in tests (GH-19575)

diff --git a/Lib/test/test_tarfile.py b/Lib/test/test_tarfile.py
index cae9680..99196f6 100644
--- a/Lib/test/test_tarfile.py
+++ b/Lib/test/test_tarfile.py
@@ -386,7 +386,7 @@
     def test_ignore_zeros(self):
         # Test TarFile's ignore_zeros option.
         # generate 512 pseudorandom bytes
-        data = Random(0).getrandbits(512*8).to_bytes(512, 'big')
+        data = Random(0).randbytes(512)
         for char in (b'\0', b'a'):
             # Test if EOFHeaderError ('\0') and InvalidHeaderError ('a')
             # are ignored correctly.