Add openbsd github action

.github/workflows/openbsd.yml

@@ -0,0 +1,25 @@
+name: openbsd
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+    runs-on: macos-12
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: make
+      uses: vmactions/openbsd-vm@v0
+      with:
+        prepare: |
+          pkg_add install -y \
+            check \
+            git \
+            pkgconf
+        run: |
+          make
+          make test