ShellCheck throws warning SC2093 when a script contains commands that could never be executed because they are after an `exec`.  Command `:` does nothing, so add it to the list of commands that don’t trigger this warning.

Using `--after-context`/`-A` or `--before-context`/`-B` would give a warning
recommending the user to use `grep -c`, even though that would give a different
result than using `grep | wc -l`:

```fundamental
$ echo -e "1\n2\n3" | grep -cA 3 1
1
$ echo -e "1\n2\n3" | grep -A 3 1 | wc -l
3
```

Using `--after-context`/`-A` or `--before-context`/`-B` would give a warning
recommending the user to use `grep -c`, even though that would give a different
result than using `grep | wc -l`:

```fundamental
$ echo -e "1\n2\n3" | grep -cA 3 1
1
$ echo -e "1\n2\n3" | grep -A 3 1 | wc -l
3
```