strip dist from upload prefix (#379)

Author: Roberto Sora

.github/workflows/nightly.yaml

@@ -27,6 +27,7 @@ jobs:
         env:
           PLUGIN_SOURCE: 'dist/*'
           PLUGIN_TARGET: '/arduino-cli/nightly'
+          PLUGIN_STRIP_PREFIX: 'dist/'
           PLUGIN_BUCKET: 'arduino-downloads-prod-beagle'
           AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID }}
           AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_ACCESS_KEY }}