CI: use new way to generate Coverity compiler config

Fixes this warning in the CI log:

[WARNING] A template configuration is recommended for this compiler.
Template configuration will become the default for this compiler in a future release.
Add "--template" to your command line, or use one of the
template configuration shortcut command lines below:
  cov-configure --gcc      # GNU C/C++ compiler (gcc/g++)
  cov-configure --msvc     # Microsoft C/C++ compiler (cl)
  cov-configure --java     # Oracle Java compiler (javac)
You must remove the specific configuration before re-running with "--template".