ci: adds GitHub Actions action.

.github/workflows/test.yml

@@ -0,0 +1,20 @@
+name: Test
+
+on:
+  push:
+
+jobs:
+  scheduled:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Check out this repo
+      uses: actions/checkout@v2
+    - name: Set up Go
+      uses: actions/setup-go@v2
+      with: {go-version: '^1.16'}
+    - name: Download dependencies
+      run: go mod download
+    - name: Build
+      run: go build ./...
+    - name: Test
+      run: go test ./...

go.mod

@@ -1,6 +1,6 @@
 module github.com/sanity-io/litter
 
-go 1.14
+go 1.16
 
 require (
 	github.com/davecgh/go-spew v0.0.0-20161028175848-04cdfd42973b // indirect