Bump pnpm/action-setup from 3 to 6

Bumps [pnpm/action-setup](https://github.com/pnpm/action-setup) from 3 to 6.
- [Release notes](https://github.com/pnpm/action-setup/releases)
- [Commits](pnpm/action-setup@v3.0.0...v6)

---
updated-dependencies:
- dependency-name: pnpm/action-setup
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/backend-tests.yml

@@ -26,7 +26,7 @@ jobs:
         with:
           repository: ether/etherpad-lite
           path: etherpad-lite
-      - uses: pnpm/action-setup@v3
+      - uses: pnpm/action-setup@v6
         name: Install pnpm
         with:
           version: 10

.github/workflows/frontend-tests.yml

@@ -15,7 +15,7 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: ether/etherpad-lite
-      - uses: pnpm/action-setup@v3
+      - uses: pnpm/action-setup@v6
         name: Install pnpm
         with:
           version: 10

.github/workflows/npmpublish.yml

@@ -31,7 +31,7 @@ jobs:
         uses: actions/checkout@v6
         with:
           repository: ether/etherpad-lite
-      - uses: pnpm/action-setup@v5
+      - uses: pnpm/action-setup@v6
         name: Install pnpm
         with:
           version: 10