Allow Go test Workflow to run on PRs

* When GitHub Workflows were refactored to draw from
a central repo, the pull_request trigger was lost
* Allow the go test/library workflow to be run on PRs
from the general public, it doesn't make use of any
sensitive materials (but it does count against my
minutes and my repo cache space)

.github/workflows/test.yaml

@@ -1,6 +1,11 @@
 name: test
 on:
   push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
 jobs:
   go:
     uses: dghubble/.github/.github/workflows/golang-library.yaml@main