GitHubActions(build job): relax branch restrictions (#3085)

Restricting CI to certain branch prevents contributors to know the
CI status of their contributions (e.g. the result from building and
running unit tests after pushing their work to their fork) before
they propose a PullRequest; because normally people create branches
when they want to start to work on something (instead of having to
use the 'main' branch of their fork).

Author: knocte

.github/workflows/build.yml

@@ -3,8 +3,7 @@ name: build
 on:
   push:
     branches:
-      - main
-      - release/*
+      - '**'
   pull_request:
     paths-ignore:
       - "**.md"