.github/workflows: use vmactions/freebsd-vm for FreeBSD (#344)

Replaces CirrusCI dependency.

.cirrus.yml

@@ -1,9 +0,0 @@
-env:
-  CIRRUS_CLONE_DEPTH: 1
-
-freebsd_12_task:
-  freebsd_instance:
-    image: freebsd-12-1-release-amd64
-  install_script: pkg install -y go
-  build_script: go build -v ./...
-  test_script: go test -race ./...

.github/workflows/test.yml

@@ -22,6 +22,23 @@ jobs:
           fetch-depth: 0
       - name: Run tests
         run: go test -race ./...
+  freebsd:
+    name: Test (FreeBSD)
+    runs-on: macos-10.15
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      - name: Run tests
+        # Unpinned Action allowed with read-only permissions.
+        uses: vmactions/freebsd-vm@v0.1.5
+        with:
+          prepare: |
+            freebsd-version
+            pkg install -y go
+            go version
+          run: go test -race ./...
   gotip:
     name: Test (Go tip)
     strategy: