Run unit tests on CI for MacOS

Though we don't officially support Apple platform, we should
at least run unit tests to make sure things are not broken.

Signed-off-by: Maksym Pavlenko <pavlenko.maksym@gmail.com>

.github/workflows/ci.yml

@@ -375,6 +375,33 @@ jobs:
           df
           losetup -l
 
+  tests-mac-os:
+    name: MacOS unit tests
+    runs-on: macos-10.15
+    timeout-minutes: 10
+    needs: [project, linters, protos, man]
+
+    steps:
+      - uses: actions/setup-go@v2
+        with:
+          go-version: '1.16.2'
+
+      - uses: actions/checkout@v2
+        with:
+          path: src/github.com/containerd/containerd
+
+      - name: Set env
+        run: |
+          echo "GOPATH=${{ github.workspace }}" >> $GITHUB_ENV
+          echo "${{ github.workspace }}/bin" >> $GITHUB_PATH
+
+      - name: Tests
+        env:
+          GOPROXY: direct
+        run: |
+          make test
+        working-directory: src/github.com/containerd/containerd
+
   cgroup2:
     name: CGroupsV2 and SELinux Integration
     # nested virtualization is only available on macOS hosts