Reverse non-zero return codes for rosdep check

[limaanto]

Hi all,
This PR builds on #948 because the behavior it implemented resulted in broken dependencies being shadowed by uninstalled packages, ie:

System dependencies have not been satisfied:
apt	REAL_PACKAGE
ERROR[PACKAGE]: Cannot locate rosdep definition for [FAKE_PACKAGE]
	rosdep key : FAKE_PACKAGE
	OS name    : ubuntu
	OS version : noble
	Data:
<no data>

yielding error code 1.

This prevented CI from distinguishing between uninstalled packages and broken dependencies.
With this PR, return code values are preserved but users can now check for error code 2 and gracefully fail instead of reading error code 1 and thinking its just a matter of installing packages.

Cheers.