.kde-ci.yml test using cppcheck

We have ignored "src/mathengine/driver.cc:13: Function parameter 'expr'
should be passed by const reference." because driver.cc seems to be
generated by a parser generator.
We have ignored "knumber/knumber_integer.cpp:87: Possible null pointer
dereference: value" because I do not know yet how to fix compiler or
static analysis warnings of type: possible NPE.