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

diff --git a/Lib/test/test_lzma.py b/Lib/test/test_lzma.py
index f24ed3c..0f3af27 100644
--- a/Lib/test/test_lzma.py
+++ b/Lib/test/test_lzma.py
@@ -350,7 +350,7 @@
     def test_decompressor_bigmem(self, size):
         lzd = LZMADecompressor()
         blocksize = 10 * 1024 * 1024
-        block = random.getrandbits(blocksize * 8).to_bytes(blocksize, "little")
+        block = random.randbytes(blocksize)
         try:
             input = block * (size // blocksize + 1)
             cdata = lzma.compress(input)