fix(ci): remove hardcoded pnpm version from workflows to resolve version conflict

pnpm/action-setup@v4 errors when both a `version` key and a `packageManager`
field in package.json are present. Removing the explicit `version: 9` /
`version: 9.12.0` from ci.yml and test.yml lets the action read pnpm@9.15.0
directly from package.json, eliminating the ERR_PNPM_BAD_PM_VERSION failure.

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

Author: ralyodio

.github/workflows/ci.yml

@@ -24,8 +24,6 @@ jobs:
       - uses: actions/checkout@v4
 
       - uses: pnpm/action-setup@v4
-        with:
-          version: 9
 
       - uses: actions/setup-node@v4
         with:

.github/workflows/test.yml

@@ -20,8 +20,6 @@ jobs:
       - uses: actions/checkout@v4
 
       - uses: pnpm/action-setup@v4
-        with:
-          version: 9.12.0
 
       - uses: actions/setup-node@v4
         with: