debootstrap: 178: arithmetic expression: expecting EOF: "baseprog 1"

[Vitaly Chikunov]

Latest debootstrap from git fails to install oracular. This is needed by mkosi@v14 creating bootabel image.

debootstrap --variant=minbase --include=ca-certificates --merged-usr --components=main,universe --arch=amd64 oracular /var/tmp/mkosi-g57jkd8g/root http://archive.ubuntu.com/ubuntu

Exits with `2`, debootstrap.log:

/usr/local/bin/debootstrap: 178: arithmetic expression: expecting EOF: "baseprog 1"

Looks like this commit created the problem
https://git.launchpad.net/ubuntu/+source/debootstrap/commit/?id=21725220e63d98107104a122b4fba868f7f1d802
```
@@ -174,7 +175,7 @@ Status: install ok installed" >> "$TARGET/var/lib/dpkg/status"
  }

  p () {
- baseprog="$(($baseprog + ${1:-1}))"
+ baseprog="$((baseprog 1))"
  }

  if ! doing_variant fakechroot; then
```

Where `baseprog 1` is not an arithmetic expression.