fix: Execute PAM authentication tests on CircleCI (#9029)

and use 'if' option of context block

.circleci/config.yml

@@ -13,6 +13,9 @@ aliases:
           ALLOW_NOPAM: true
           CONTINUOUS_INTEGRATION: true
           DISABLE_SIMPLECOV: true
+          PAM_ENABLED: true	
+          PAM_DEFAULT_SERVICE: pam_test	
+          PAM_CONTROLLED_SERVICE: pam_test_controlled
     working_directory: ~/projects/mastodon/
 
   - &attach_workspace