Default antora displayVersion

Issue gh-10765

docs/antora/extensions/version-fix.js

@@ -18,6 +18,9 @@ module.exports.register = function({ config }) {
                 aggregate.displayVersion = `${aggregate.version}`
                 delete aggregate.prerelease
             }
+            if (aggregate.prerelease === "true" && !aggregate.displayVersion) {
+                aggregate.displayVersion = `${aggregate.version}`
+            }
         })
     })
 }