Fix rpm_key absent. (#31045)

When keyid is 8 charactes long, drop_key function cuts everything
issuing an error: "package gpg-pubkey- is not installed"

lib/ansible/modules/packaging/os/rpm_key.py

@@ -183,7 +183,7 @@ class RpmKey(object):
 
     def drop_key(self, keyid):
         if not self.module.check_mode:
-            self.execute_command([self.rpm, '--erase', '--allmatches', "gpg-pubkey-%s" % keyid[8:].lower()])
+            self.execute_command([self.rpm, '--erase', '--allmatches', "gpg-pubkey-%s" % keyid[-8:].lower()])
 
 
 def main():