don't run Actions on pushes to main

don't run Actions on pushes to main

This mays seem odd, but I usually push to dev and build there, and only merge
back into main when I want to do a release - and in that case I push to main
and push a tag, which now causes two Actions to kick off. This way we reduce
the number of redundant builds...

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>