Fix endPage() not updating the printer block state

This meant that we didn't show the bottom slot was full until other
items were moved in the inventory.

projects/common/src/main/java/dan200/computercraft/shared/peripheral/printer/PrinterBlockEntity.java

@@ -225,7 +225,9 @@ public final class PrinterBlockEntity extends AbstractContainerBlockEntity imple
         var stack = PrintoutItem.createSingleFromTitleAndText(pageTitle, lines, colours);
         for (var slot : BOTTOM_SLOTS) {
             if (inventory.get(slot).isEmpty()) {
-                setItem(slot, stack);
+                inventory.set(slot, stack);
+                updateBlockState();
+                setChanged();
                 printing = false;
                 return true;
             }