Install pnpm globally in build and release workflows

Added 'npm i -g pnpm' to both build and release GitHub Actions workflows to ensure pnpm is available before running installation and build commands.

.github/workflows/release.yml

@@ -17,6 +17,7 @@ jobs:
           node-version: 20.x
       - name: Build NapCat.Framework
         run: |
+          npm i -g pnpm
           pnpm i
           pnpm --filter napcat-webui-frontend run build || exit 1
           pnpm run build:framework
@@ -39,6 +40,7 @@ jobs:
           node-version: 20.x
       - name: Build NapCat.Shell
         run: |
+          npm i -g pnpm
           pnpm i
           pnpm --filter napcat-webui-frontend run build || exit 1
           pnpm run build:shell