Fix MicroBuildOutputFolderOverride on publishing of BootstrapperInfo.json (#5711)

Author: donnie-msft

eng/pipelines/templates/pipeline.yml

@@ -133,7 +133,7 @@ stages:
       - output: pipelineArtifact
         displayName: 'Publish BootstrapperInfo.json as a build artifact'
         condition: "and(succeeded(), eq(variables['BuildRTM'], 'false'))"
-        targetPath: ${env:MicroBuildOutputFolderOverride}\MicroBuild\Output
+        targetPath: $(MicroBuildOutputFolderOverride)\MicroBuild\Output
         artifactName: MicroBuildOutputs
 
       - output: artifactsDrop