Fix string formatting further in DocPreviewCleanup.yml

Author: abhro

.github/workflows/DocPreviewCleanup.yml

@@ -40,7 +40,7 @@ jobs:
 
           function all_prs()
               url = "https://api.github.com/repos/$repo/pulls?per_page=100;page="
-              query_prs(page) = JSON3.read(HTTP.get(url * page).body)
+              query_prs(page) = JSON3.read(HTTP.get(url * string(page)).body)
               prs = []
               page = 1
               while true