ci: disable workflow for next branch

Changes in `semantic-release` seem to make it difficult to publish pre-releases
into `lint-staged@next`, so disable it for now. For more info, see the following PR:
#1265

Author: iiroj

.github/workflows/main.yml

@@ -5,7 +5,6 @@ on:
     # Run on pushes to specific branches
     branches:
       - master
-      - next
       - beta
       - alpha
     # Do not run on tags