cp: Adding dd to SELinux CI to enable cp-a-selinux

[ChrisDryden]

The GNU test cp-a-selinux was failing previously, but after the optimization to reduce the amount of built bins in the SELinux GNU CI it began skipping this test because this test relied on dd to setup the test. By adding this back the test moves from SKIP to FAIL and I have a followup PR with the fixes to make this test PASS

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tty/tty-eof (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/shuf/shuf-reservoir (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/sort/sort-stale-thread-mem (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/cp/cp-a-selinux was skipped on 'main' but is now failing.