xtask: run tests with +nightly

This avoids needing to manually override the default toolchain with `rustup override`. Also fix an out-of-date comment.

Author: nicholasbishop

xtask/src/main.rs

@@ -94,10 +94,9 @@ fn run_host_tests() -> Result<()> {
  let cargo = Cargo {
  action: CargoAction::Test,
  features: vec![Feature::Exts],
- nightly: false,
+ nightly: true,
  // Don't test uefi-services (or the packages that depend on it)
- // as it has lang items that conflict with `std`. The xtask
- // currently doesn't have any tests.
+ // as it has lang items that conflict with `std`.
  packages: vec![Package::Uefi, Package::UefiMacros, Package::Xtask],
  release: false,
  // Use the host target so that tests can run without a VM.