Fix isPrerelease variable usage

Author: dibarbet

azure-pipelines/release.yml

@@ -78,6 +78,7 @@ extends:
                 displayName: 'Install vsce'
               - task: AzureCLI@2
                 displayName: '🚀 Publish to Marketplace'
+                name: PublishToMarketplaceStep
                 inputs:
                   azureSubscription: 'VSCode Marketplace Publishing'
                   scriptType: "pscore"
@@ -112,10 +113,10 @@ extends:
                     If ( $uploadPrerelease ) {
                       $basePublishArgs += "--pre-release"
                       Write-Host "Publish to pre-release channel."
-                      Write-Host "##vso[task.setvariable variable=isPrerelease]true"
+                      Write-Host "##vso[task.setvariable variable=isPrerelease;isOutput=true]true"
                     } Else {
                       Write-Host "Publish to release channel."
-                      Write-Host "##vso[task.setvariable variable=isPrerelease]false"
+                      Write-Host "##vso[task.setvariable variable=isPrerelease;isOutput=true]false"
                     }
                     $basePublishArgs += '--azure-credential'
                     $basePublishArgs += '--packagePath'
@@ -141,6 +142,9 @@ extends:
       displayName: 'Tag release of vscode-csharp'
       dependsOn: 'PublishStage'
       condition: succeeded('PublishStage')
+      variables:
+      - name: isPrerelease
+        value: $[ stageDependencies.PublishStage.PublishToMarketplace.outputs['PublishToMarketplaceStep.isPrerelease'] ]
       jobs:
       - job: 'Tag'
         pool: