panic trying to run script, when script is given with just a filename

[jruderman]

cargo-bisect-rustc --script timeout.sh

panics after the first download:

checking nightly-2022-10-26 from the currently installed default nightly toolchain as the last failure
checking the start range to find a passing nightly
installing nightly-2022-10-26
testing...
thread 'main' panicked at 'thiserror::Errored to run "timeout.sh": Os { code: 2, kind: NotFound, message: "No such file or directory" }', /Users/jruderman/.cargo/registry/src/gb.xjqchip.workers.dev-1ecc6299db9ec823/cargo-bisect-rustc-0.6.4/src/toolchains.rs:302:17
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

It should either work, or give an error message earlier saying I need to add the ./ prefix.

(The name and contents of the script don't matter for this bug; an empty script or one with just a shebang line is enough to trigger it.)

Contrast: actually missing script

cargo-bisect-rustc --script notfound.sh

gives a reasonable, early error message:

error: Invalid value "notfound.sh" for '--script <SCRIPT>': No such file or directory (os error 2)

Contrast: prefix script name with ./

cargo-bisect-rustc --script ./timeout.sh

works.