printList: Force item before determining whether to print multi-line

src/libexpr/print.cc

@@ -377,6 +377,9 @@ private:
         }
     }
 
+    /**
+     * @note This may force items.
+     */
     bool shouldPrettyPrintList(std::span<Value * const> list)
     {
         if (!options.shouldPrettyPrint() || list.empty()) {
@@ -393,6 +396,9 @@ private:
             return true;
         }
 
+        // It is ok to force the item(s) here, because they will be printed anyway.
+        state.forceValue(*item, item->determinePos(noPos));
+
         // Pretty-print single-item lists only if they contain nested
         // structures.
         auto itemType = item->type();

tests/functional/repl/pretty-print-idempotent.expected

@@ -14,9 +14,7 @@ Added <number omitted> variables.
   layerOne = { ... };
 }
 
-[
+[ "https://example.com" ]
-  "https://example.com"
-]
 
 [ "https://example.com" ]