Fix GitHub Actions unit tests workflow

* Default branch was renamed from master to main
* Internal build and publishing workflows were unaffected,
the GitHub Action is just for public contribution vetting

.github/workflows/test.yaml

@@ -1,11 +1,6 @@
 name: test
 on:
   push:
-    branches:
-      - master
-  pull_request:
-    branches:
-      - master
 jobs:
   build:
     name: go