ci(unit): fix unit tests CI to use pnpm

.github/workflows/test.yml

@@ -14,24 +14,24 @@ jobs:
     steps:
       - uses: actions/checkout@v3
 
+      - uses: pnpm/action-setup@v2
+        # uses version from "packageManager" field in package.json
+
       - name: Setup Node.js ${{ matrix.node-version }}
         uses: actions/setup-node@v3
         with:
-          cache: yarn
+          cache: pnpm
           node-version: ${{ matrix.node-version }}
 
-      - name: Install Yarn
-        run: npm i yarn --global
-
       - name: Install Packages
         run: |
-          yarn install --frozen-lockfile
+          pnpm install --frozen-lockfile
         env:
           CYPRESS_CACHE_FOLDER: .cache/Cypress
 
       - name: Run Unit Tests
         run: |
-          yarn ci --coverage
+          pnpm run ci --coverage
 
       - name: Upload Coverage to Coveralls
         # it feels a bit weird to use @master, but that's what the docs use