README: show rpi-6.12.y build status

Remove rpi-5.15.y build status since it doesn't appear to be built anymore, and add rpi-6.12.y build status.

Author: marcone

README.md

@@ -17,14 +17,14 @@ Please read the Documentation/process/changes.rst file, as it contains the
 requirements for building and running the kernel, and information about
 the problems which may result by upgrading your kernel.
 
-Build status for rpi-5.15.y:
-[![Pi kernel build tests](https://github.com/raspberrypi/linux/actions/workflows/kernel-build.yml/badge.svg?branch=rpi-5.15.y)](https://github.com/raspberrypi/linux/actions/workflows/kernel-build.yml)
-[![dtoverlaycheck](https://github.com/raspberrypi/linux/actions/workflows/dtoverlaycheck.yml/badge.svg?branch=rpi-5.15.y)](https://github.com/raspberrypi/linux/actions/workflows/dtoverlaycheck.yml)
-
 Build status for rpi-6.1.y:
 [![Pi kernel build tests](https://github.com/raspberrypi/linux/actions/workflows/kernel-build.yml/badge.svg?branch=rpi-6.1.y)](https://github.com/raspberrypi/linux/actions/workflows/kernel-build.yml)
 [![dtoverlaycheck](https://github.com/raspberrypi/linux/actions/workflows/dtoverlaycheck.yml/badge.svg?branch=rpi-6.1.y)](https://github.com/raspberrypi/linux/actions/workflows/dtoverlaycheck.yml)
 
 Build status for rpi-6.6.y:
 [![Pi kernel build tests](https://github.com/raspberrypi/linux/actions/workflows/kernel-build.yml/badge.svg?branch=rpi-6.6.y)](https://github.com/raspberrypi/linux/actions/workflows/kernel-build.yml)
 [![dtoverlaycheck](https://github.com/raspberrypi/linux/actions/workflows/dtoverlaycheck.yml/badge.svg?branch=rpi-6.6.y)](https://github.com/raspberrypi/linux/actions/workflows/dtoverlaycheck.yml)
+
+Build status for rpi-6.12.y:
+[![Pi kernel build tests](https://github.com/raspberrypi/linux/actions/workflows/kernel-build.yml/badge.svg?branch=rpi-6.12.y)](https://github.com/raspberrypi/linux/actions/workflows/kernel-build.yml)
+[![dtoverlaycheck](https://github.com/raspberrypi/linux/actions/workflows/dtoverlaycheck.yml/badge.svg?branch=rpi-6.12.y)](https://github.com/raspberrypi/linux/actions/workflows/dtoverlaycheck.yml)