test-fs-util: re-order test_readlink_and_make_absolute and test_get_files_in_director...

test-fs-util: re-order test_readlink_and_make_absolute and test_get_files_in_directory (#6288)

test_readlink_and_make_absolute switches to a temp directory, and then
removes it.

test_get_files_in_directory calls opendir(".") from a directory that has
been removed from the filesystem.

This call sequence triggers a bug in Gentoo's sandbox library. This
library attempts to resolve the "." to an absolute path, and aborts when
it ultimately fails to do so.

Re-ordering the calls works around the issue until the sandbox library
can be fixed to more gracefully deal with this.

Bug: https://bugs.gentoo.org/590084