Always use virtual machines for agents

jenkins-infra/helpdesk#4490 notes that
Windows builds for plugins that use container agents are not starting.

https://status.jenkins.io/issues/2025-01-08-ci.jenkins.io-azure-outage/
reports the outage is due to an Azure Container Instance (ACI) outage
in the region where we host the ci.jenkins.io agents.

vars/buildPlugin.groovy

@@ -15,6 +15,8 @@ def call(Map params = [:]) {
   def useArtifactCachingProxy = params.containsKey('useArtifactCachingProxy') ? params.useArtifactCachingProxy : true
 
   def useContainerAgent = params.containsKey('useContainerAgent') ? params.useContainerAgent : false
+  // TODO: Remove when https://github.com/jenkins-infra/helpdesk/issues/4490 is resolved
+  useContainerAgent = false
   def forkCount = params.containsKey('forkCount') ? params.forkCount : null
   if (forkCount) {
     echo "Running parallel tests with forkCount=${forkCount}"