ci: Use pnpm version from package.json

Remove pnpm version from  CI workflows to use the version specified in the root package.json's `packageManager` property.
This property is set by npm corepack.

Also update the pnpm setup actions and pin them to a fixed commit hash.

Author: lucas-koehler

.github/workflows/ci.yaml

@@ -28,11 +28,10 @@ jobs:
         with:
           node-version: 18
 
-      - uses: pnpm/action-setup@v4.0.0
+      - uses: pnpm/action-setup@a7487c7e89a18df4991f7f222e4898a00d66ddda # v4.1.0
         name: Install pnpm
         id: pnpm-install
         with:
-          version: 8
           run_install: false
 
       - name: Build

.github/workflows/publish.yaml

@@ -42,11 +42,10 @@ jobs:
           node-version: "18"
           registry-url: "https://registry.npmjs.org"
 
-      - uses: pnpm/action-setup@v4.0.0
+      - uses: pnpm/action-setup@a7487c7e89a18df4991f7f222e4898a00d66ddda # v4.1.0
         name: Install pnpm
         id: pnpm-install
         with:
-          version: 8
           run_install: false
 
       - name: "Install Packages"