manifest: update LVGL to v8.4.0

Related to zephyrproject-rtos/lvgl#51

Signed-off-by: Fabian Blatz <fabianblatz@gmail.com>

west.yml

@@ -274,7 +274,7 @@ manifest:
       revision: 1bf2120cffcedae174ae35d695a28a46caefcb23
       path: modules/lib/loramac-node
     - name: lvgl
-      revision: 2b76c641749725ac90c6ac7959ca7718804cf356
+      revision: 2b498e6f36d6b82ae1da12c8b7742e318624ecf5
       path: modules/lib/gui/lvgl
     - name: mbedtls
       revision: 6ec4abdcda78dfc47315af568f93e5ad4398dea0