Add continue-on-error for cache saving

Author: marxin

.github/workflows/ci.yml

@@ -63,6 +63,7 @@ jobs:
       - name: Save cached Linkcheck
         id: cache-linkcheck-save
         if: github.event_name == 'schedule'
+        continue-on-error: true
         uses: actions/cache/save@v4
         with:
           path: book/linkcheck/cache.json

ci/linkcheck.sh

@@ -8,7 +8,7 @@ set_github_token() {
 }
 
 # https://docs.github.com/en/actions/reference/environment-variables
-if [ yes ] ; then # running in scheduled job
+if [ "$GITHUB_EVENT_NAME" = "schedule" ] ; then # running in scheduled job
   FLAGS=""
   USE_TOKEN=1