Run most of our test suite with Secure Boot enabled
UEFI Secure Boot restricts some operations that would otherwise be allowed and has thus potential to break stuff, due to kernel lockdown (see #17493).
Once we support Secure Boot, it could be that we start seeing problems
that are hard to understand/reproduce because they only occur when
Secure Boot is enabled.
Running as much as we can of our test suite with Secure Boot enabled would mitigate this problem.