Fix the verifier setup in gradle, and update to use the latest verifier jar version

[jwren]

The version needs to be updated for sure. https://github.com/JetBrains/intellij-plugin-verifier/releases/tag/1.384

I think that the issue that broke it is two fold: some of the refactoring for 2025.1 broke the ability for it to run for the Flutter IJ plugin.

Also, when I updated the version the last time around, the jar wasn't in the PR, glancing at the .gitignore file, I think this was the issue. #7871

cc @pq