…ull request.

Cache the conda environment to speed up the build across subsequent runs.
Data files in tudat-resources are not cached. They are downloaded
separately in an event of a cache hit.
Failing tests in MacOS are temporarily ignored to let the workflow pass
and the cache feature to be tested.

ccache works out of the box for the GNU compilers in Ubuntu and the
Clang compiler in MacOS. The MSVC compilers require an extra
configuration step which was added to the CMakeLists file.

Feature/add ccache

Rename the ccache step to describe what it does.
Fix typo in referencing the matrix variable build type.

…se proceeds with the build step. Caching of compilation results of the current run happens post completion of the build step.

…o a feature branch that is also a source in a pull request