Fixes shellcheck warning reported in
https://github.com/coder/coder/pull/21496#discussion_r2696470065
## Problem
The `error()` function in `lib.sh` already calls `exit 1`, so the `exit
1` on line 17 of `check_pg_schema.sh` was unreachable:
```
In ./scripts/check_pg_schema.sh line 17:
exit 1
^----^ SC2317 (info): Command appears to be unreachable.
```
## Solution
Remove the redundant `exit 1` since `error()` already handles exiting.
Co-authored-by: blink-so[bot] <211532188+blink-so[bot]@users.noreply.github.com>
