Add main version

Author: spencer@primus

.github/workflows/test_on_main.yml

@@ -9,7 +9,7 @@ on:
 jobs:
   call_tester:
     name: Run unit tests on main branch
-    uses: avstack-lab/avstack-core/.github/workflows/test_on_branch.yml
+    uses: avstack-lab/avstack-core/.github/workflows/test_on_branch.yml@main
     with:
       branch: main
       os: ubuntu-22.04

.github/workflows/test_on_workflows.yml

@@ -9,7 +9,7 @@ on:
 jobs:
   call_tester:
     name: Run unit tests on workflows branch
-    uses: avstack-lab/avstack-core/.github/workflows/test_on_branch.yml
+    uses: avstack-lab/avstack-core/.github/workflows/test_on_branch.yml@main
     with:
       branch: workflows
       os: ubuntu-22.04