fix: remove explicit pnpm from CI matrix to avoid version conflict

siguici/setup-js passes version:latest to pnpm/action-setup, which
conflicts with packageManager field in package.json. The "" (auto-detect)
matrix entry already covers pnpm via the packageManager field.

Author: thejackshelton

.github/workflows/ci.yml

@@ -21,7 +21,7 @@ jobs:
         os: [ubuntu-latest, macos-latest, windows-latest]
         experimental: [false]
         runtime: [node, deno, bun]
-        pm: ["", pnpm, yarn]
+        pm: ["", yarn]
 
     steps:
       - uses: actions/checkout@v4