If UID and GID don't match, build fails

Failure message:

```
 > [runner 3/7] RUN useradd -m -u 1000 -g 999 patuser:
#8 3.853 useradd: group '999' does not exist
------
executor failed running [/bin/sh -c useradd -m -u ${UID} -g ${GID} patuser]: exit code: 6
```