ci(web): pin pnpm to 11.3.0 in setup

The floating "version: 11" in pnpm/action-setup resolved to 11.12.0,
whose self-installer crashes with "Cannot use 'in' operator to search
for 'integrity' in undefined" and fails the Validate job. Pin to 11.3.0
to match the local dev version that generated the lockfile.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 236dddd8-bdf2-4e0a-ac56-0ce8ab98d88e

Author: AchoArnold

.github/workflows/web.yml

@@ -34,7 +34,7 @@ jobs:
       - uses: pnpm/action-setup@v6
         name: Install pnpm
         with:
-          version: 11
+          version: 11.3.0
 
       - name: Install dependencies 📦
         run: pnpm install
@@ -66,7 +66,7 @@ jobs:
       - uses: pnpm/action-setup@v6
         name: Install pnpm
         with:
-          version: 11
+          version: 11.3.0
 
       - name: Install dependencies 📦
         run: pnpm install