Improve workflow files

[yutaro-sakamoto]

This pull request improves ci.yml and cppcheck.yml.

• Remove unnecessary environment variables and dependencies defined in ci.yml.
• Remove unncessary code in cppcheck.yml.
• Change a job name in cppcheck.yml to cppcheck.

These changes are inspired by @GitMensch's comments.

[GitMensch]

You may want to run either two builds - one --with-db and one --with-vbisam or have both as separate steps in the the test/run.

If you opt for the first you don't need libdb-dev in one, not vbisam in the other; if you opt for the later then you'd duplicate the steps but would mkdir build_db && cd build_db && ../configure ...; in any case I suggest to not run the make install for gnucobol as the tests should use the gnucobol built, not the gnucobol installed.