Added GitHub Action for testing (#6)

* Added GitHub Action for testing

- Triggered when there is a push or pr to main. Can also be triggered manually.
- Uses the go version as specified in the go.mod file.

* Add test build to workflow

Author: Ricky White

.github/workflows/test.yml

@@ -0,0 +1,25 @@
+name: Test
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Set up Go
+        uses: actions/setup-go@v4
+        with:
+          go-version-file: "go.mod"
+
+      - name: Test Build
+        run: go build -v -o ssh-sign ./cmd/ssh-sign/main.go
+
+      - name: Test
+        run: go test -v ./...