build: add GitHub actions config for unit tests

* build: add GitHub actions config for unit tests

* chore: link root directory before linting

* chore: also need to npm i

Author: bcoe

packages/google-cloud-node/package.json

@@ -39,7 +39,8 @@
     "predocs-test": "npm run docs",
     "compile": "tsc -p . && cp system-test/*.js build/system-test/ && cp -r protos build/",
     "prepare": "npm run compile",
-    "pretest": "npm run compile"
+    "pretest": "npm run compile",
+    "prelint": "cd samples; npm link ../; npm i"
   },
   "dependencies": {
     "@google-cloud/common": "^2.0.0",