README: show rpi-6.4.y build status

6.2 is EOL, and 6.5 hasn't been released yet, so show the 6.4 build status.

Author: pelwell

README.md

@@ -25,6 +25,6 @@ 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-6.2.y:
-[![Pi kernel build tests](https://github.com/raspberrypi/linux/actions/workflows/kernel-build.yml/badge.svg?branch=rpi-6.2.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-6.2.y)](https://github.com/raspberrypi/linux/actions/workflows/dtoverlaycheck.yml)
+Build status for rpi-6.4.y:
+[![Pi kernel build tests](https://github.com/raspberrypi/linux/actions/workflows/kernel-build.yml/badge.svg?branch=rpi-6.4.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-6.4.y)](https://github.com/raspberrypi/linux/actions/workflows/dtoverlaycheck.yml)