Store built configuration for CI testing
The main.tar is bundled confiugration file from jcs-emacs.
We attempted to use filename {{ matrix.os }}.{{ matrix.emacs-version }}.tar;
but it will instantly kills our 1G of LFS quota. Hence we have only one built
file from each platforms and Emacs versions.
Before we explode our large file storge (LFS), our strategy here is to revert
anything to our very first main .tar file's commit using the
git reset --hard <commit_id> command. Then we force push git push --force
our tar file to this repository, in order to make our LFS' disk space low.