fix: correct yOffset for trapdoors to be a bit lower

Tested in 1.8.8 and 1.21.1 and in both versions the offset
was too low. So I've changed it a bit.

modules/betterchairs-api/src/main/java/de/sprax2013/betterchairs/ChairUtils.java

@@ -118,7 +118,7 @@ public static double getSitOffset(Block block, boolean sitsOnArmorStand, ChairNM
         XMaterial blockType = XMaterial.matchXMaterial(block.getType());
 
         if (blockType.name().endsWith("_TRAPDOOR")) {
-            yOffset = -0.125;
+            yOffset = -0.25;
         }
 
         return -1.2 + yOffset + (sitsOnArmorStand ? 0 : 1);