Adapt cppcheck output parser to cppcheck v1.90
The GitLab runner machine previously ran Ubuntu 18.04, which featured cppcheck 1.82. Some planned enhancements to the CI scripts required a newer version of cppcheck, so we have upgraded it to Ubuntu 20.04, which has cppcheck 1.90. However, the format of the diagnostics printed by cppcheck has changed in 1.90, so our code that parsed them needs adapting to match.