fix: race in delete user functionality (#13547)

- The race happens with a goroutine that refreshes IAM cache data from storage.
- It could lead to deleted users re-appearing as valid live credentials.
- This change also causes CI to run tests without a race flag (in addition to
running it with).

cmd/admin-handlers-users_test.go

@@ -32,7 +32,7 @@ import (
 )
 
 const (
-	testDefaultTimeout = 10 * time.Second
+	testDefaultTimeout = 30 * time.Second
 )
 
 // API suite container for IAM