ci: enable corepack in npm preview build

The actions/setup-node@v4 action fails because it cannot
correctly use corepack.

To fix that I implemented workaround. It installs corepack
via npm and then enables it.

We cannot remove it, because pkg.pr.new needs
corepack in order to work.

See: actions/setup-node#1222 (comment)

Author: Haberkamp

.github/workflows/npm-preview-release.yml

@@ -11,7 +11,7 @@ jobs:
     steps:
       - name: Checkout code
         uses: actions/checkout@v2
-      - run: corepack enable
+      - run: npm i -g --force corepack && corepack enable
       - uses: actions/setup-node@v4
         with:
           node-version: 20