pkg/cli/admin/upgrade/recommend: Don't error on unaccepted issues when the feature gate is off

When OC_ENABLE_CMD_UPGRADE_RECOMMEND_ACCEPT is not set to true, the
--accept option does not exist.  In that case, we don't want to error
with [1]:

  error: issues that apply to this cluster but which were not included in --accept: ConditionalUpdateRisk

Instead, we just want to exit happily, because we've already mentioned
the issue earlier in the message.

[1]: https://prow.ci.openshift.org/view/gs/test-platform-results/pr-logs/pull/29831/pull-ci-openshift-origin-main-e2e-aws-ovn-serial-1of2/1951653929842380800

Author: wking

pkg/cli/admin/upgrade/recommend/examples/4.12.16-longest-not-recommended.version-4.12.51-output

@@ -15,5 +15,3 @@ Reason: MultipleReasons
 Message: An unintended reversion to the default kubelet nodeStatusReportFrequency can cause significant load on the control plane. https://issues.redhat.com/browse/MCO-1094
 
   After rebooting into kernel-4.18.0-372.88.1.el8_6 or later, kernel nodes experience high load average and io_wait times. The nodes might fail to start or stop pods and probes may fail. Workload and host processes may become unresponsive and workload may be disrupted. https://issues.redhat.com/browse/COS-2705
-
-error: issues that apply to this cluster but which were not included in --accept: AlertNoTestData,ConditionalUpdateRisk

pkg/cli/admin/upgrade/recommend/examples/4.12.16-longest-recommended.version-4.12.51-output

@@ -15,5 +15,3 @@ Reason: MultipleReasons
 Message: An unintended reversion to the default kubelet nodeStatusReportFrequency can cause significant load on the control plane. https://issues.redhat.com/browse/MCO-1094
 
   After rebooting into kernel-4.18.0-372.88.1.el8_6 or later, kernel nodes experience high load average and io_wait times. The nodes might fail to start or stop pods and probes may fail. Workload and host processes may become unresponsive and workload may be disrupted. https://issues.redhat.com/browse/COS-2705
-
-error: issues that apply to this cluster but which were not included in --accept: AlertNoTestData,ConditionalUpdateRisk

pkg/cli/admin/upgrade/recommend/examples/4.16.27-degraded-monitoring.version-4.16.32-output

@@ -23,5 +23,3 @@ Channel: candidate-4.16 (available channels: candidate-4.16, candidate-4.17, can
 Update to 4.16.32 has no known issues relevant to this cluster.
 Image: quay.io/openshift-release-dev/ocp-release@sha256:0e71cb61694473b40e8d95f530eaf250a62616debb98199f31b4034808687dae
 Release URL: https://access.redhat.com/errata/RHSA-2025:0650
-
-error: issues that apply to this cluster but which were not included in --accept: ClusterOperatorDown,Failing,PodDisruptionBudgetAtLimit

pkg/cli/admin/upgrade/recommend/recommend.go

@@ -342,10 +342,12 @@ func (o *options) Run(ctx context.Context) error {
 						issues.Insert("ConditionalUpdateRisk")
 					}
 					unaccepted := issues.Difference(accept)
-					if unaccepted.Len() > 0 {
-						return fmt.Errorf("issues that apply to this cluster but which were not included in --accept: %s", strings.Join(sets.List(unaccepted), ","))
-					} else if issues.Len() > 0 && !o.quiet {
-						fmt.Fprintf(o.Out, "Update to %s has no known issues relevant to this cluster other than the accepted %s.\n", update.Release.Version, strings.Join(sets.List(issues), ","))
+					if kcmdutil.FeatureGate("OC_ENABLE_CMD_UPGRADE_RECOMMEND_ACCEPT").IsEnabled() {
+						if unaccepted.Len() > 0 {
+							return fmt.Errorf("issues that apply to this cluster but which were not included in --accept: %s", strings.Join(sets.List(unaccepted), ","))
+						} else if issues.Len() > 0 && !o.quiet {
+							fmt.Fprintf(o.Out, "Update to %s has no known issues relevant to this cluster other than the accepted %s.\n", update.Release.Version, strings.Join(sets.List(issues), ","))
+						}
 					}
 					return nil
 				}