test/install-content/hook.sh: only require a bootname for non-bootloader slots
test/install-content/hook.sh: only require a bootname for non-bootloader slots

This was not noticed because the CI checks were changed to run the coverage
check directly, which caused test errors to be ignored.

Signed-off-by: Jan Luebbe <3a82f1ac4ad59607a20f180f1c67ac8ba31ad0d5@pengutronix.de>

ejoerns/rauc,ejoerns/rauc,jluebbe/rauc,jluebbe/rauc,rauc/rauc,jluebbe/rauc,rauc/rauc,rauc/rauc,ejoerns/rauc