ICI: Remove caching of workspace

[christophfroehlich]

Fixes #33 the easiest way: just don't cache the workspace, but only ccache directory.

Does it make sense to cache the workspace at all, how much is the speed benefit compared to only caching ccache?

• Locally, it takes 20s vs 2min if I remove the build folder.
• cache vs no cache of ros2_control binary build: The ICI step takes the same time.

This also resolved some weird include errors while updating an upstream dependency in ros-controls/ros2_control#1485 (yes, we could delete the caches manually but still..)

[saikishor]

LGTM as all checks are green!

[fmauch]

Wait - if we remove the target_ws cache we do not increase build time? Then I really think this is worth going that route.

[christophfroehlich]

Wait - if we remove the target_ws cache we do not increase build time? Then I really think this is worth going that route.

Please verify that once again 😄 but the two workflow runs I've linked above don't show any difference.

[christophfroehlich]

Also for semi-binary builds, the build-step of ICI takes approx 30s only with/without cache (the upstream workspace was not cached anyways).