tests: test_fileio.py: don't follow symlinks in /dev (#626)

There might be a broken one like /dev/log and this causes the tests to fail.

This is highly is unpredictable, because os.scandir() sometimes returns a block device, sometimes the broken link is hit.

So pass follow_symlinks=False to entry.stat().

tests/test_fileio.py

@@ -218,7 +218,7 @@ async def test_is_block_device(self) -> None:
         assert not await Path("/btelkbee").is_block_device()
         with os.scandir("/dev") as iterator:
             for entry in iterator:
-                if stat.S_ISBLK(entry.stat().st_mode):
+                if stat.S_ISBLK(entry.stat(follow_symlinks=False).st_mode):
                     assert await Path(entry.path).is_block_device()
                     break
             else: