chore: Add pre-release flag to pipeline (#1180)

.azure-pipelines/vscode-gradle-nightly.yml

@@ -95,7 +95,7 @@ steps:
     path: $(Build.SourcesDirectory)/extension
 - bash: |
     cd $(Build.SourcesDirectory)/extension
-    npx vsce@latest package
+    npx vsce@latest package --pre-release
   displayName: Package VSIX
 - task: CopyFiles@2
   displayName: Copy VSIX