docs: bump the arm compiler version

Patch fdae0b95852e087d8a19187f4d40babc67f0e57a in the CI bumped it to
6.23. Reflect this in docs

Change-Id: I39f3cd6fb03f81066fbbae3672c79802c607e3cd
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
1 file changed