https://github.com/NixOS/nixpkgs/pull/321484 introduced a bug when when
`forceFetchGit=true`.
This PR revert the change only for this case.
The previous PR made work cases like:
```bash
nix-build -E 'let pkgs = import ./nixpkgs {}; in pkgs.fetchFromGitHub {
owner = "<username>"; repo = "<repo>"; rev = "HEAD"; hash = "";
private=true; forceFetchGit=false; }'
```
You should see the download working and nix complaining about hash
mismatch.
Now if you take the case where `forceFetchGit=true`, this is a different
story:
```
nix-build -E 'let pkgs = import ./nixpkgs {}; in pkgs.fetchFromGitHub {
owner = "<username>"; repo = "<repo>"; rev = "HEAD"; hash = "";
private=true; forceFetchGit=true; }'
```
Logs look like:
```
Initialized empty Git repository in /nix/store/<hash>-source/.git/
fatal: could not read Username for 'https://github.com': No such device or address
fatal: could not read Username for 'https://github.com': No such device or address
fatal: could not read Username for 'https://github.com': No such device or address
fatal: could not read Username for 'https://github.com': No such device or address
Unable to checkout HEAD from https://github.com/<username>/<repo>.git.
```
I was using `forceFetchGit` for the exact reason the previous PR was
made, I will move to `forceFetchGit=false` now.
Still the previous PR was a broke usage of `fetchFromGitHub` force private repository when `forceFetchGit` is used.
f19cf904b1