chore: install npm via npm, not pnpm, so the release step's publish action resolves bundled deps [skip ci]

Author: jkeen

.github/actions/pnpm/action.yml

@@ -9,7 +9,7 @@ runs:
         cache: 'pnpm'
     - name: 'Ensure latest npm'
       shell: 'bash'
-      run: pnpm add -g npm@latest
+      run: npm install -g npm@latest
     - name: 'Install dependencies'
       shell: 'bash'
       run: pnpm install