Validate if only 1 image policy selector is given

Signed-off-by: Hidde Beydals <hello@hidde.co>

cmd/flux/create_image_policy.go

@@ -102,7 +102,9 @@ func createImagePolicyRun(cmd *cobra.Command, args []string) error {
 
 	switch {
 	case imagePolicyArgs.semver != "" && imagePolicyArgs.alpha != "":
-		return fmt.Errorf("policy cannot be specified with both --select-semver and --select-alpha")
+	case imagePolicyArgs.semver != "" && imagePolicyArgs.numeric != "":
+	case imagePolicyArgs.alpha != "" && imagePolicyArgs.numeric != "":
+		return fmt.Errorf("only one of --select-semver, --select-alpha or --select-numeric can be specified")
 	case imagePolicyArgs.semver != "":
 		policy.Spec.Policy.SemVer = &imagev1.SemVerPolicy{
 			Range: imagePolicyArgs.semver,