pin pnpm/action-setup version to 6.0.8

Author: infeo

.github/workflows/gh-pages.yml

@@ -19,7 +19,7 @@ jobs:
       with:
         hugo-version: '0.148.1'
         extended: true
-    - uses: pnpm/action-setup@v4 #TODO
+    - uses: pnpm/action-setup@0e279bb959325dab635dd2c09392533439d90093 # v6.0.8
     - uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4.4.0
       with:
         node-version: 22