fix: contracts testing workflow failure due to kleros-app resolution in yarn hardened mode

.github/workflows/contracts-testing.yml

@@ -38,16 +38,23 @@ jobs:
           registry.yarnpkg.com:443
           registry.npmjs.org:443
           54.185.253.63:443
-
-    - name: Setup Node.js environment
-      uses: actions/setup-node@39370e3970a6d050c480ffad4ff0ed4d3fdee5af # v4.1.0
-      with:
-        node-version: 18.x   
 
     - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
       with:
         submodules: recursive
-
+
+    - name: Set up corepack (for yarn)
+      run: |
+        corepack enable
+        corepack prepare yarn@4.5.1 --activate
+        yarn set version 4.5.1
+
+    - name: Setup Node.js environment
+      uses: actions/setup-node@39370e3970a6d050c480ffad4ff0ed4d3fdee5af # v4.1.0
+      with:
+        node-version: 20.x   
+        cache: yarn
+
     - name: Cache node modules
       uses: actions/cache@1bd1e32a3bdc45362d1e726936510720a7c30a57 # v4.2.0
       env:
@@ -61,7 +68,9 @@ jobs:
           ${{ runner.os }}-build-${{ secrets.CACHE_VERSION }}-${{ env.cache-name }}-
 
     - name: Install contracts dependencies
-      run: yarn workspace @kleros/kleros-v2-contracts install
+      run: |
+        # TODO: re-enable hardened mode once the kleros-app resolution is fixed
+        YARN_ENABLE_HARDENED_MODE=0 yarn workspace @kleros/kleros-v2-contracts install
 
     - name: Install Foundry
       uses: foundry-rs/foundry-toolchain@8f1998e9878d786675189ef566a2e4bf24869773 # v1.2.0