Cover edge case when on new minor release for E2E upgrade test (#10781)

.drone.yml

@@ -644,6 +644,10 @@ steps:
         UPGRADE_CHANNEL="latest"
       else
         UPGRADE_CHANNEL=$(echo $DRONE_BRANCH | sed 's/release-/v/')
+        # Check if the UPGRADE_CHANNEL exists, in the case of new minor releases it won't
+        if ! curl --head --silent --fail https://update.k3s.io/v1-release/channels/$UPGRADE_CHANNEL; then
+          UPGRADE_CHANNEL="latest"
+        fi
       fi
       E2E_RELEASE_CHANNEL=$UPGRADE_CHANNEL go test -v -timeout=45m ./upgradecluster_test.go  -ci -local
       cp ./coverage.out /tmp/artifacts/upgrade-coverage.out