ci: first attempt at general bits and bobs...

Obviously given the state of github yaml-engineering there's
no way I'm going to get this right on the first try
but hey ho. things *should* work.

.github/workflows/common.yml

@@ -0,0 +1,38 @@
+name: Common CI/CD
+
+on:
+  push:
+    branches:
+      - "main"
+    paths:
+      - "common/**"
+  pull_request:
+    branches:
+      - "main"
+    paths:
+      - "common/**"
+  workflow_dispatch:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - uses: pnpm/action-setup@v2
+        with:
+          version: 7.20.0
+
+      - uses: actions/setup-node@v3
+        with:
+          node-version: 16
+          cache: pnpm
+
+      - name: Install dependencies
+        run: pnpm --filter tachi-common... --filter . install
+
+      - name: Run Tests
+        run: pnpm --filter tachi-common test
+        env:
+          NODE_ENV: "test"