Fix typo in check_str for system_admin policy rule

Story: #2010435
Task: #46851
Depends-On: https://review.opendev.org/c/openstack/requirements/+/865276
Change-Id: I4896f1508e34785864c260e64484ae0138100ef4
(cherry picked from commit 455057c)

barbican/common/policies/base.py

@@ -24,7 +24,7 @@
         check_str='role:reader and system_scope:all'),
     policy.RuleDefault(
         name='system_admin',
-        check_str='role:amdin and system_scope:all'),
+        check_str='role:admin and system_scope:all'),
 
     policy.RuleDefault(
         name='secret_project_match',