In that case it specified $doc output but didn't even create it.
I expect it's better to do it this way instead of creating it
as an empty directory.
(Only the failed builds get rebuilt by this commit.)
This will install the HTML and text documentation into a separate output
so that users can install it without having to rebuild Git.
Previously only `doc/git/git-subtree.html` was installed (which is now
in $doc as well).
The current output sizes are as follows:
```
$ du -sh $(nix-build -A git)
47M /nix/store/wyqgalp61kmavx06rams7z8jz177nd8y-git-2.26.2
$ du -sh $(nix-build -A git.doc)
14M /nix/store/6zi22fl5xc3sg23d9shsviinvwk89wvq-git-2.26.2-doc
```
Fixes#86022 (at least partly since the output has to be installed).
###### Motivation for this change
Update to latest upstream version
###### Things done
* [ ] Tested using sandboxing ([nix.useSandbox](http://nixos.org/nixos/manual/options.html#opt-nix.useSandbox) on NixOS, or option `sandbox` in [`nix.conf`](http://nixos.org/nix/manual/#sec-conf-file) on non-NixOS linux)
* Built on platform(s)
* [x] NixOS
* [ ] macOS
* [ ] other Linux distributions
* [ ] Tested via one or more NixOS test(s) if existing and applicable for the change (look inside [nixos/tests](https://github.com/NixOS/nixpkgs/blob/master/nixos/tests))
* [ ] Tested compilation of all pkgs that depend on this change using `nix-shell -p nix-review --run "nix-review wip"`
* [x] Tested execution of all binary files (usually in `./result/bin/`)
* [ ] Determined the impact on package closure size (by running `nix path-info -S` before and after)
* [ ] Ensured that relevant documentation is up to date
* [x] Fits [CONTRIBUTING.md](https://github.com/NixOS/nixpkgs/blob/master/.github/CONTRIBUTING.md).
###### Notify maintainers
cc @worldofpeace @tfc @jtraue
@the-kenny did a good job in the past and is set as maintainer in many package,
however since 2017-2018 he stopped contributing. To create less confusion
in pull requests when people try to request his feedback, I removed him as
maintainer from all packages.
