tests/functional: fixed 062

?? which is appeared in 062 could make test result unstable.
This is becuase ?? will be assumed as wildcare of filename.

For example, if there is a file named 'fi' in the directory,
?? will return 'fi' but not '??'. So the test will fail.

This patch fixed the problem by replace ?? to ^^.

Signed-off-by: Kai Zhang <kyle@zelin.io>
Signed-off-by: Liu Yuan <namei.unix@gmail.com>