Avoid two builds on prereleases (#1441)

Author: ssbarnea

.github/workflows/tox.yml

@@ -11,7 +11,6 @@ on:
   release:
     types:
     - published  # It seems that you can publish directly without creating
-    - prereleased
   schedule:
   - cron: 1 0 * * *  # Run daily at 0:01 UTC
   # Run every Friday at 18:02 UTC