message: Make test less brittle prior to assert_eq failure message format change
  PR on Rust is to make assert_eq error message be multi-line. Before implementing this we need to make the current test less brittle.
diff: @@ -242,10 +242,10 @@ fn cargo_bench_failing_test() {
  [FINISHED] release [optimized] target(s) in [..]
  [RUNNING] target[/]release[/]deps[/]foo-[..][EXE]
  thread '[..]' panicked at 'assertion failed: \
  - `(left == right)` (left: \
  - `\"hello\"`, right: `\"nope\"`)', src[/]foo.rs:14
  -[..]
  -", p.url()))
  + `(left == right)`", p.url()))
  + .with_stderr_contains("left: `\"hello\"`")
  + .with_stderr_contains("right: `\"nope\"`")
  + .with_stderr_contains("src[/]foo.rs:14")
  .with_status(101));
  }
  