CI: set ubuntu version to 24.04
Use a specific version of Ubuntu instead of `rolling' to fix our CI. [Backport commit 16f52544.] Signed-off-by:Vincent Stehlé <vincent.stehle@arm.com>
Use a specific version of Ubuntu instead of `rolling' to fix our CI. [Backport commit 16f52544.] Signed-off-by:Vincent Stehlé <vincent.stehle@arm.com>