fix(ci): remove pnpm version conflict in action-setup

pnpm/action-setup@v4 now errors when both the action's `version` input
and package.json's `packageManager` field specify a version. Remove the
action input — package.json's `pnpm@9.15.4` is authoritative.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -14,8 +14,6 @@ jobs:
       - uses: actions/checkout@v4
 
       - uses: pnpm/action-setup@v4
-        with:
-          version: 9
 
       - uses: actions/setup-node@v4
         with:
@@ -38,8 +36,6 @@ jobs:
       - uses: actions/checkout@v4
 
       - uses: pnpm/action-setup@v4
-        with:
-          version: 9
 
       - uses: actions/setup-node@v4
         with:
@@ -60,8 +56,6 @@ jobs:
       - uses: actions/checkout@v4
 
       - uses: pnpm/action-setup@v4
-        with:
-          version: 9
 
       - uses: actions/setup-node@v4
         with: