fix(nodepool): propagate osImageStream validation error to caller

The nilerr linter flagged that validateOSImageStream error was checked
but the function returned nil instead of the error. Propagate the error
to match the pattern used by other validation failures in the same
function.

Signed-off-by: Salvatore Dario Minonne <sminonne@redhat.com>
Commit-Message-Assisted-by: Claude (via Claude Code)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: sdminonne

hypershift-operator/controllers/nodepool/conditions.go

@@ -394,7 +394,7 @@ func (r *NodePoolReconciler) validMachineConfigCondition(ctx context.Context, no
 			Message:            err.Error(),
 			ObservedGeneration: nodePool.Generation,
 		})
-		return &ctrl.Result{}, nil
+		return &ctrl.Result{}, fmt.Errorf("failed to validate osImageStream: %w", err)
 	}
 
 	SetStatusCondition(&nodePool.Status.Conditions, hyperv1.NodePoolCondition{

hypershift-operator/controllers/nodepool/osstream_test.go

@@ -13,7 +13,7 @@ import (
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 )
 
-func TestGetRHELStream(t *testing.T) {
+func Test_getRHELStream(t *testing.T) {
 	testCases := []struct {
 		name           string
 		nodePool       *hyperv1.NodePool