ci(audit-signatures): install the latest corepack so the latest npm signing key is available

Author: travi

.github/workflows/test.yml

@@ -37,6 +37,7 @@ jobs:
           node-version: "${{ matrix.node-version }}"
           cache: npm
       - run: npm clean-install
+      - run: npm install --global corepack@latest
       - run: corepack npm audit signatures
       - run: npm test