Packaging: Ensure upgrade_is_oss flag file is always deleted (#30732)

This commit ensures the delete of the upgrade_is_oss indicator for
the packaging tests is always deleted before each run. It works by
moving the check on version which skips the task into the doFirst block,
replacing the onlyIf.

closes #30682

buildSrc/src/main/groovy/org/elasticsearch/gradle/vagrant/VagrantTestPlugin.groovy

@@ -11,6 +11,7 @@ import org.gradle.api.internal.artifacts.dependencies.DefaultProjectDependency
 import org.gradle.api.tasks.Copy
 import org.gradle.api.tasks.Delete
 import org.gradle.api.tasks.Exec
+import org.gradle.api.tasks.StopExecutionException
 import org.gradle.api.tasks.TaskState
 
 class VagrantTestPlugin implements Plugin<Project> {
@@ -188,8 +189,10 @@ class VagrantTestPlugin implements Plugin<Project> {
             dependsOn copyPackagingArchives
             doFirst {
                 project.delete("${archivesDir}/upgrade_is_oss")
+                if (project.extensions.esvagrant.upgradeFromVersion.before('6.3.0')) {
+                    throw new StopExecutionException("upgrade version is before 6.3.0")
+                }
             }
-            onlyIf { project.extensions.esvagrant.upgradeFromVersion.onOrAfter('6.3.0') }
             file "${archivesDir}/upgrade_is_oss"
             contents ''
         }