2.2234 serial form incompatibility

[jglick]

CloudBees-internal issue

For automated testing: #766 (comment): this seems like a cleaner way to run the test—can handle actual agents, and no need to commit binary files.

jenkinsci/kubernetes-plugin#1656 successfully verified via CloudBees proprietary integration test.

Manual testing in Docker-related plugins noted in downstream PRs.

[jglick]

Note that this trick only works once:

diff --git pipeline-model-definition/src/test/java/org/jenkinsci/plugins/pipeline/modeldefinition/UpgradeTest.java pipeline-model-definition/src/test/java/org/jenkinsci/plugins/pipeline/modeldefinition/UpgradeTest.java
index 5f3b783f..095ebc62 100644
--- pipeline-model-definition/src/test/java/org/jenkinsci/plugins/pipeline/modeldefinition/UpgradeTest.java
+++ pipeline-model-definition/src/test/java/org/jenkinsci/plugins/pipeline/modeldefinition/UpgradeTest.java
@@ -118,6 +118,10 @@ public final class UpgradeTest {
                 var b = p.getBuildByNumber(1);
                 r.waitForMessage("Resuming build at ", b);
                 r.waitForMessage("Ready to run at ", b);
+            });
+            rr.then(r -> {
+                var p = r.jenkins.getItemByFullName("p", WorkflowJob.class);
+                var b = p.getBuildByNumber(1);
                 var proceed = Path.of(((StringParameterValue) b.getAction(ParametersAction.class).getParameter("PROCEED")).getValue());
                 System.err.println("Touching " + proceed);
                 Files.writeString(proceed, "go");