DEV: Update workflow for core pnpm change (#123)

Author: davidtaylorhq

.github/workflows/update_docs.yml

@@ -60,21 +60,8 @@ jobs:
           bundle install --jobs 4
           bundle clean
 
-      - name: Get yarn cache directory
-        id: yarn-cache-dir
-        run: echo "::set-output name=dir::$(yarn cache dir)"
-
-      - name: Yarn cache
-        uses: actions/cache@v3
-        id: yarn-cache
-        with:
-          path: ${{ steps.yarn-cache-dir.outputs.dir }}
-          key: ${{ runner.os }}-yarn-${{ hashFiles('**/yarn.lock') }}
-          restore-keys: |
-            ${{ runner.os }}-yarn-
-
-      - name: Yarn install
-        run: yarn install
+      - name: pnpm install
+        run: pnpm install
 
       - name: Create and migrate database
         run: |