CI: replace deprecated `set-output` with `echo`

.github/workflows/main.yml

@@ -30,10 +30,15 @@ jobs:
         with:
           version: 7
           run_install: false
+      - name: Get pnpm store directory
+        id: pnpm-cache
+        shell: bash
+        run: |
+          echo "STORE_PATH=$(pnpm store path)" >> $GITHUB_OUTPUT
       - uses: actions/cache@v3
         name: Setup pnpm cache
         with:
-          path: ${{ steps.pnpm-cache.outputs.pnpm_cache_dir }}
+          path: ${{ steps.pnpm-cache.outputs.STORE_PATH }}
           key: ${{ runner.os }}-pnpm-store-${{ hashFiles('**/pnpm-lock.yaml') }}
           restore-keys: |
             ${{ runner.os }}-pnpm-store-