Remove registry-url from setup-node, rely on npm OIDC trusted publishing for auth

[pcholakov]

Summary

• Drops registry-url from actions/setup-node in the publish workflow
• When registry-url is set, setup-node creates a temp .npmrc with _authToken=${NODE_AUTH_TOKEN}; if that var is set (e.g. to GITHUB_TOKEN by the runner), npm uses the token instead of doing an OIDC exchange
• Without registry-url, no .npmrc with an auth token ref is created; npm falls through to OIDC trusted publishing automatically
• Registry URL is already declared in package.json via publishConfig["@restatedev:registry"] so nothing is lost
• NPM_TOKEN repository secret is no longer needed

Test plan

• Merge and observe the next snapshot publish succeeds without NPM_TOKEN