fix(ci): correct variable name from ub_level to sub_level

The variable name was incorrectly set as ub_level in the kernel-custom.yml workflow. This change corrects it to sub_level to match the intended configuration parameter.

.github/workflows/kernel-custom.yml

@@ -45,7 +45,7 @@ jobs:
           variant: "Hakan"
         - android_version: "android14"
           kernel_version: "6.1"
-          ub_level: "68"
+          sub_level: "68"
           os_patch_level: "2024-03"
           variant: "Duchamp"