Handle empty message in Progressing=True condition of CO status

The job [1] spotted a corner case where CO emitted the empty message
when it reports Progressing=True. The empty message is not idea but
seem legit since the field is optional [2]. The reason field could
also be empty but I do not see any CO popping up like it.

A unit test is added to cover this case. The input of the case is
taken from [3].

[1]. https://prow.ci.openshift.org/view/gs/test-platform-results/pr-logs/pull/30154/pull-ci-openshift-origin-main-e2e-aws-ovn-single-node-upgrade/1960354194137288704

[2]. https://github.com/openshift/api/blob/94481d71bb6f3ce6019717ea7900e6f88f42fa2c/config/v1/types_cluster_operator.go#L145

[2]. https://gcsweb-ci.apps.ci.l2s4.p1.openshiftapps.com/gcs/test-platform-results/pr-logs/pull/30154/pull-ci-openshift-origin-main-e2e-aws-ovn-single-node-upgrade/1960354194137288704/artifacts/e2e-aws-ovn-single-node-upgrade/single-node-e2e-test/artifacts/junit/adm-upgrade-status/adm-upgrade-status-2025-08-26%2016:59:14.041315708%20+0000%20UTC%20m=+773.120136531__20250826-164647.txt

Author: hongkailiu

pkg/monitortests/cli/adm_upgrade/status/controlplane.go

@@ -10,7 +10,7 @@ import (
 )
 
 var (
-	operatorFirstLinePattern = regexp.MustCompile(`^\S+\s+\S+\s+\S+\s+.*$`)
+	operatorFirstLinePattern = regexp.MustCompile(`^\S+\s+\S+\s+\S+(\s+.*)?$`)
 )
 
 func (w *monitor) controlPlane() *junitapi.JUnitTestCase {

pkg/monitortests/cli/adm_upgrade/status/controlplane_test.go

@@ -134,6 +134,28 @@ ip-10-0-64-121.ec2.internal   Outdated     Pending   4.20.0-0.ci-2025-08-13-1748
 SINCE    LEVEL   IMPACT   MESSAGE
 24m12s   Info    None     Update is proceeding well`
 
+var operatorsWithEmptyMessage = `Unable to fetch alerts, ignoring alerts in 'Update Health':  failed to get alerts from Thanos: no token is currently in use for this session
+= Control Plane =
+Assessment:      Progressing
+Target Version:  4.20.0-0.ci-2025-08-26-154705-test-ci-op-jy9dt0lx-latest (from 4.20.0-0.ci-2025-08-26-145530-test-ci-op-jy9dt0lx-initial)
+Updating:        authentication
+Completion:      9% (3 operators updated, 1 updating, 30 waiting)
+Duration:        7m27s (Est. Time Remaining: 36m)
+Operator Health: 32 Healthy, 1 Unavailable, 1 Available but degraded
+
+Updating Cluster Operators
+NAME             SINCE   REASON                 MESSAGE
+authentication   58s     WellKnownReadyCon...   
+
+Control Plane Nodes
+NAME                                       ASSESSMENT   PHASE     VERSION                                                     EST   MESSAGE
+ip-10-0-35-68.us-east-2.compute.internal   Outdated     Pending   4.20.0-0.ci-2025-08-26-145530-test-ci-op-jy9dt0lx-initial   ?     
+
+= Update Health =
+SINCE   LEVEL   IMPACT   MESSAGE
+7m27s   Info    None     Update is proceeding well
+`
+
 var controlPlaneCompleted = `Unable to fetch alerts, ignoring alerts in 'Update Health':  failed to get alerts from Thanos: no token is currently in use for this session
 = Control Plane =
 Update to 4.20.0-0.ci-2025-08-13-182454-test-ci-op-5wilvz46-latest successfully completed at 2025-08-13T20:33:32Z (duration: 59m)
@@ -236,6 +258,15 @@ func TestMonitor_ControlPlane(t *testing.T) {
 				Name: "[sig-cli][OCPFeatureGate:UpgradeStatus] oc adm upgrade status control plane section is consistent",
 			},
 		},
+		{
+			name: "operators section with empty message",
+			snapshots: []snapshot{
+				{when: time.Now(), out: operatorsWithEmptyMessage},
+			},
+			expected: &junitapi.JUnitTestCase{
+				Name: "[sig-cli][OCPFeatureGate:UpgradeStatus] oc adm upgrade status control plane section is consistent",
+			},
+		},
 		{
 			name: "control plane completed",
 			snapshots: []snapshot{