fix: Change search string for multiversion doc selector

.github/workflows/build-check-install.yaml

@@ -354,7 +354,7 @@ jobs:
             echo "ref-name=${{ steps.branch-name.outputs.current_branch }}" >> $GITHUB_OUTPUT
           fi
           # Check if pkgdown multiversion docs are used at all.
-          if [ $(grep -rl '<!-- start dropdown for versions -->' gh-pages | wc -l) -gt 0 ]; then
+          if [ $(grep -rl '<!-- Generated by pkgdown + https://github.com/insightsengineering/r-pkgdown-multiversion -->' gh-pages | wc -l) -gt 0 ]; then
             echo "multiversion-docs=true" >> $GITHUB_OUTPUT
           else
             echo "multiversion-docs=false" >> $GITHUB_OUTPUT