ci: bump pnpm action to v11 (etherpad core requires pnpm >=11.1.2)

Author: JohnMcLear

.github/workflows/backend-tests.yml

@@ -32,7 +32,7 @@ jobs:
       - uses: pnpm/action-setup@v4
         name: Install pnpm
         with:
-          version: 10
+          version: 11
           run_install: false
       - name: Get pnpm store directory
         shell: bash

.github/workflows/npmpublish.yml

@@ -30,7 +30,7 @@ jobs:
       - uses: pnpm/action-setup@v4
         name: Install pnpm
         with:
-          version: 10
+          version: 11
           run_install: false
       - name: Get pnpm store directory
         shell: bash
@@ -81,7 +81,7 @@ jobs:
       - uses: pnpm/action-setup@v4
         name: Install pnpm
         with:
-          version: 10
+          version: 11
           run_install: false
       - name: Get pnpm store directory
         shell: bash