Updated Test workflow to use re-usable template

refs https://github.com/TryGhost/actions@main/.github/workflows/test.yml

- this commit switches CI to using a re-usable workflow to reduce
  duplication and make repositories easier to maintain

Author: daniellockyer

.github/workflows/test.yml

@@ -6,27 +6,7 @@ on:
       - main
       - 'renovate/*'
 jobs:
-  build:
-    runs-on: ubuntu-18.04
-    if: github.event_name == 'push' || (github.event_name == 'pull_request' && !startsWith(github.head_ref, 'renovate/'))
-    strategy:
-      matrix:
-        node: [ '12', '14' ]
-    name: Node ${{ matrix.node }}
-    steps:
-      - uses: actions/checkout@v2
-      - uses: actions/setup-node@v2
-        with:
-          node-version: ${{ matrix.node }}
-      - run: yarn global add lerna
-      - run: yarn
-      - run: yarn test
-
-      - uses: codecov/codecov-action@v2
-
-      - uses: daniellockyer/action-slack-build@master
-        if: failure() && github.event_name == 'push' && github.ref == 'refs/heads/main'
-        with:
-          status: ${{ job.status }}
-        env:
-          SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_URL }}
+  test:
+    uses: tryghost/actions/.github/workflows/test.yml@main
+    secrets:
+      SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_URL }}