CI: switch off the nightly release builds (#4145)

This CI workflow has been failing for some time, and I get a notification every night.
There is no need to waste your GitHub Actions budget on this.

Author: mzabaluev

.github/workflows/release.yml

@@ -1,6 +1,4 @@
 on:
-  schedule:
-    - cron: '0 3 * * *' # Nightly, run at 03:00 UTC
   push:
     tags:
       - 'v[0-9]+.*' # Release tags matching v*, i.e. v1.0, v20.15.10