Closed issue by Piraty on void-packages repository

https://github.com/void-linux/void-packages/issues/20393

Description:
### Expected behavior
xbps-src doesn't care if run from the main repo or a worktree
### Actual behavior
xbps-src complains about not being run from a git repository a lot during builds.
```
fatal: not a git repository: <...>
```

I'm not 100% sure it leads to fatal build errors, but I remember to see build failures happen in worktrees which didn't occur when building in the main repo (I have yet to find a case to prove this); this might have been related to incorrect SOURCE_DATE_EPOCH derivation or similar...

### Steps to reproduce the behavior
```
cd void-packages

branch=random-branch
main_repo="$(pwd)"

git branch $branch ; git worktree add /tmp/VOID-$branch $branch
cd /tmp/VOID-$branch $branch

# bootstrap using main hostdir (to not fetch binary-bootstrap again)
XBPS_HOSTDIR="$main_repo/hostdir" ./xbps-src binary-bootstrap
./xbps-src pkg which
```