denylist: snooze ssh.key until new afterburn release

Extend the snooze on the `coreos.ignition.ssh.key` test failure
for another month until a new release of Afterburn can be
performed that will include the fix for the failure:
coreos/afterburn#1074.

A release is pending in:
coreos/afterburn#1095

kola-denylist.yaml

@@ -7,7 +7,7 @@
   tracker: https://github.com/coreos/coreos-assembler/pull/1478
 - pattern: coreos.ignition.ssh.key
   tracker: https://github.com/coreos/fedora-coreos-tracker/issues/1553
-  snooze: 2024-08-01
+  snooze: 2024-09-01
   warn: true
   platforms:
     - azure