docs: Fix ReadTheDocs sphinx.configuration requirement #612

Job	Run time
raspberrypi/rpi-test-image/poky/systemd	11s
raspberrypi0-2w-64/rpi-test-image/poky/systemd	11s
raspberrypi0-2w/rpi-test-image/poky/systemd	12s
raspberrypi0/rpi-test-image/poky/systemd	11s
raspberrypi0-wifi/rpi-test-image/poky/systemd	12s
raspberrypi2/rpi-test-image/poky/systemd	12s
raspberrypi3-64/rpi-test-image/poky/systemd	12s
raspberrypi3/rpi-test-image/poky/systemd	11s
raspberrypi4-64/rpi-test-image/poky/systemd	11s
raspberrypi4/rpi-test-image/poky/systemd	11s
raspberrypi5/rpi-test-image/poky/systemd	11s
raspberrypi-cm3/rpi-test-image/poky/systemd	11s
raspberrypi-cm/rpi-test-image/poky/systemd	11s
raspberrypi-armv7/rpi-test-image/poky/systemd	11s
raspberrypi-armv8/rpi-test-image/poky/systemd	12s
	2m 50s

Provide feedback