Use same Node.js version as the action environment for tests

Node.js 12 is the newest version available for the JavaScript GitHub Actions actions, and is the one in use, as specified
in action.yml's `runs.using` key. So it is best to use the same when running the tests in the CI workflow.

Author: per1234

.github/workflows/test-typescript-task.yml

@@ -22,7 +22,7 @@ jobs:
       - name: Set Node.js 10.x
         uses: actions/setup-node@v2
         with:
-          node-version: 10.x
+          node-version: 12.x
 
       - name: Install Task
         uses: arduino/actions/setup-taskfile@master