ci: only generate semantic tags on main branch
Created by: bobheadxi
See INC-47. As a result of us switching to semantic versions in deploy-sourcegraph-dot-com (see: https://github.com/sourcegraph/deploy-sourcegraph-dot-com/commit/1399713cb525b7e346a8e73663473a95df9d3c74), we lost the previous guard against unexpected deployments from other branches that we had when we used insiders
.
This changes the pipeline to only generate these semantic versions in main
, otherwise it encodes the branch into the tag.