Update kernel-a15.yml: Add 6.6.87

.github/workflows/kernel-a15.yml

@@ -42,6 +42,8 @@ jobs:
             os_patch_level: "2025-03"
           - sub_level: "82"
             os_patch_level: "2025-04"
+          - sub_level: "87"
+            os_patch_level: "2025-05"
           - sub_level: "X"
             os_patch_level: "lts"
     uses: ./.github/workflows/build.yml