`doom-cli-upgrade` calls `git fetch` to fetch remote branch and tags and
check output code of this command to complain when it failed.
It fails when remote server isn't available that is good.
But it also fails when it can't to fast-forward a branch that will be
used to upgrade doom-emacs.
The last case created a loop and the only way to broke this loop is
remote a branch that should be used for upgrade.
Unfortunately user has no idea about branch name and can't do anything,
just enjoy crash with `Failed to fetch from upstream` message.
This commit added `--force` flag to `git fetch` that forces it to
overwrite branch that is used to upgrade that prevent such loop.
It also fixed https://github.com/hlissner/doom-emacs/issues/4346
be923535fa