package/openssh: add CVE ignore for CVE-2024-6387
Commit ecc0c1fb1244 (package/openssh: disable async-signal-unsafe code in
sshsigdie()) add a patch for CVE-2024-6387 but forgot to add an _IGNORE_CVES
entry. Fix that.
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>