workflows: build: add kernel v6.12 to build-checks

Kernel v6.12 has been release recently, add this to the regular
build-upstream-ubuntu checks.

Signed-off-by: Louis Peens <[email protected]>
Reviewed-by: Ryno Swart <[email protected]>

.github/workflows/build.yaml

@@ -383,6 +383,7 @@ jobs:
         release: [
           { name: "net-next",  runs-on: "20.04", },
           { name: "net",       runs-on: "20.04", },
+          { name: "6.12",      runs-on: "20.04", },
           { name: "6.11",      runs-on: "20.04", },
           { name: "6.10",      runs-on: "20.04", },
           { name: "6.9",       runs-on: "20.04", },