Fix terminal output getting cut-off by one character

[kylewlacy]

Here's a screenshot from a failed build showing what renders in my terminal (set with a width of 80 characters)

Note the message in the middle, which clearly has a letter cut off in the word "backtrace":

note: run with `RUST_BACKTRACE=1` environment variable to display a
acktrace

There is likely an off-by-one error somewhere in in the console reporter code (permalink). The console reporter uses the superconsole crate under the hood. This doesn't affect the plain terminal output (e.g. when running brioche build 2>&1 | cat)