CI: Fail on cppcheck.sh error

[hdiethelm]

Fix issue in cppcheck.sh and make CI fail on cppcheck error

Additionally, make shellckeck.sh failing except for files that need yet to be fixed.

[hdiethelm]

Fails as expected:
https://github.com/LinuxCNC/linuxcnc/actions/runs/26900235217/job/79350299474?pr=4119
Next try.

[hdiethelm]

Still failing but the CI doesn't build my code but probably the one it would get after merge. The failing line doesn't look like this in my branch:
https://github.com/hdiethelm/linuxcnc-fork/blob/cppcheck_fail/src/hal/drivers/mesa-hostmot2/hm2_eth.c#L532

@BsAtHome That is what I was talking about in the other thread. Now the CI fails when there are cppcheck issues, so you dont't have to complain any more, the CI does it for you. There was a bug in cppcheck.sh

This can only be merged after the issue in #4111 got fixed and merged, otherwise the CI on master will fail.

Let's see if I can easily add a warn only list to shellcheck.sh. You can remove it as soon as all issues are fixed.

[hdiethelm]

And the shellcheck warn/error variant.
I just wanted to test if it works. If you think it's useless, I can revert this commit before merge.

This now generates CI errors except for the following files:

./scripts/rip-environment.in \
./scripts/realtime.in \
./scripts/linuxcnc_info.in \
./docs/src/asciideps \
./debian/update-dch-from-git \

This will help against creping in issues in other shell scripts and as soon as these files are fixed, you can remove the code again or also just remove the files from the list.

[hdiethelm]

And after some mocking around with the github ci there is even a nice annotation:

[hdiethelm]

^Rebased back to master