capi: aws: report all conflicting user tags at once

Returning an error for each tag means a user would have to run the
Installer multiple times to find out all the clobbered tags. Let's
include all the conflicts at once in the error message.

Also changed from the deprecated set syntax to the new generics style.

Author: r4f4

pkg/asset/machines/aws/awsmachines.go

@@ -3,7 +3,6 @@ package aws
 
 import (
 	"fmt"
-	"sort"
 
 	v1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -130,21 +129,21 @@ func CapaTagsFromUserTags(clusterID string, usertags map[string]string) (capa.Ta
 	tags := capa.Tags{}
 	tags[fmt.Sprintf("kubernetes.io/cluster/%s", clusterID)] = "owned"
 
-	forbiddenTags := sets.NewString()
+	forbiddenTags := sets.New[string]()
 	for key := range tags {
 		forbiddenTags.Insert(key)
 	}
 
-	userTagKeys := make([]string, 0, len(usertags))
+	userTagKeys := sets.New[string]()
 	for key := range usertags {
-		userTagKeys = append(userTagKeys, key)
+		userTagKeys.Insert(key)
 	}
-	sort.Strings(userTagKeys)
 
-	for _, k := range userTagKeys {
-		if forbiddenTags.Has(k) {
-			return nil, fmt.Errorf("user tags may not clobber %s", k)
-		}
+	if clobberedTags := userTagKeys.Intersection(forbiddenTags); clobberedTags.Len() > 0 {
+		return nil, fmt.Errorf("user tag keys %v are not allowed", sets.List(clobberedTags))
+	}
+
+	for _, k := range sets.List(userTagKeys) {
 		tags[k] = usertags[k]
 	}
 	return tags, nil