fix: scan every GraphQL error for the active-clusters conflict

[ianaya89]

IsActiveClustersError returned from inside the loop on the first CONFLICT-coded error:

if code, ok := gqlError.Extensions["code"]; ok && code == "CONFLICT" {
    return strings.Contains(gqlError.Message, "forceDestroyClusters=true"), nil
}

When the API reports two conflicts and the active-clusters one is not first, the function answers false and never looks at the rest. FormatDeleteError then falls back to dumping the raw GraphQL messages instead of telling the user to set force_destroy_clusters=true.

Now the code and message are matched together and the loop keeps scanning, which is what IsNotFoundError already does.

TestIsActiveClustersError_ConflictAfterOtherConflict fails on master and passes with the fix. The five existing cases still pass.