Change yarn caching in GitHub Actions to allow partial caching

Previously it was all or nothing, so a single change will
have to re-download everything.
Now it works the same as local, only downloading the one new package.

.github/actions/setup/action.yml

@@ -0,0 +1,22 @@
+name: Node Setup & Yarn Install
+description: 'Setup Node.js and install dependencies with Yarn'
+runs:
+  using: composite
+  steps:
+    - uses: actions/setup-node@v3
+      with:
+        node-version: 20
+
+    - name: Yarn cache
+      uses: actions/cache@v3
+      with:
+        path: .yarn/cache
+        key: yarn-cache-${{ hashFiles('yarn.lock', '.yarnrc.yml') }}
+        restore-keys: yarn-cache-
+
+    - name: Install dependencies
+      shell: bash
+      run: yarn install
+      env:
+        # Use the local cache folder, so we can cache it above
+        YARN_ENABLE_GLOBAL_CACHE: 'false'

.github/workflows/ci.yml

@@ -21,13 +21,12 @@ jobs:
 
     steps:
       - uses: actions/checkout@v3
-      - uses: actions/setup-node@v3
-        with:
-          node-version: 20
-          cache: yarn
 
-      - name: Install dependencies
-        run: yarn install && yarn dedupe --check
+      - name: Node Setup & Yarn Install
+        uses: ./.github/actions/setup
+
+      - name: Check for no duplicate dependencies
+        run: yarn dedupe --check
 
       - name: Match API PR
         uses: actions-ecosystem/action-regex-match@v2