Fix based on changes to yield_now

[Darksonn]

Due to tokio-rs/tokio#5223, some metrics tests were broken. These need to be fixed.

failures:

---- src/task.rs - task::TaskMetrics::mean_scheduled_duration (line 1924) stdout ----
Test executable failed (exit status: 101).

stderr:
thread 'main' panicked at 'assertion failed: interval.mean_scheduled_duration() >= Duration::from_secs(1)', src/task.rs:34:5
stack backtrace:
   0: rust_begin_unwind
             at /rustc/fc594f15669680fa70d255faec3ca3fb507c3405/library/std/src/panicking.rs:575:5
   1: core::panicking::panic_fmt
             at /rustc/fc594f15669680fa70d255faec3ca3fb507c3405/library/core/src/panicking.rs:64:14
   2: core::panicking::panic
             at /rustc/fc594f15669680fa70d255faec3ca3fb507c3405/library/core/src/panicking.rs:111:5
   3: rust_out::main::{{closure}}
   4: <core::pin::Pin<P> as core::future::future::Future>::poll
   5: tokio::runtime::scheduler::current_thread::CoreGuard::block_on::{{closure}}::{{closure}}::{{closure}}
   6: tokio::runtime::scheduler::current_thread::CoreGuard::block_on::{{closure}}::{{closure}}
   7: tokio::runtime::scheduler::current_thread::Context::enter
   8: tokio::runtime::scheduler::current_thread::CoreGuard::block_on::{{closure}}
   9: tokio::runtime::scheduler::current_thread::CoreGuard::enter::{{closure}}
  10: tokio::macros::scoped_tls::ScopedKey<T>::set
  11: tokio::runtime::scheduler::current_thread::CoreGuard::enter
  12: tokio::runtime::scheduler::current_thread::CoreGuard::block_on
  13: tokio::runtime::scheduler::current_thread::CurrentThread::block_on
  14: tokio::runtime::runtime::Runtime::block_on
  15: rust_out::main
  16: core::ops::function::FnOnce::call_once
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.


---- src/task.rs - task::TaskMetrics::total_scheduled_duration (line 922) stdout ----
Test executable failed (exit status: 101).

stderr:
thread 'main' panicked at 'assertion failed: total_scheduled_duration >= Duration::from_millis(1000)', src/task.rs:30:5
stack backtrace:
   0: rust_begin_unwind
             at /rustc/fc594f15669680fa70d255faec3ca3fb507c3405/library/std/src/panicking.rs:575:5
   1: core::panicking::panic_fmt
             at /rustc/fc594f15669680fa70d255faec3ca3fb507c3405/library/core/src/panicking.rs:64:14
   2: core::panicking::panic
             at /rustc/fc594f15669680fa70d255faec3ca3fb507c3405/library/core/src/panicking.rs:111:5
   3: rust_out::main::{{closure}}
   4: <core::pin::Pin<P> as core::future::future::Future>::poll
   5: tokio::runtime::scheduler::current_thread::CoreGuard::block_on::{{closure}}::{{closure}}::{{closure}}
   6: tokio::runtime::scheduler::current_thread::CoreGuard::block_on::{{closure}}::{{closure}}
   7: tokio::runtime::scheduler::current_thread::Context::enter
   8: tokio::runtime::scheduler::current_thread::CoreGuard::block_on::{{closure}}
   9: tokio::runtime::scheduler::current_thread::CoreGuard::enter::{{closure}}
  10: tokio::macros::scoped_tls::ScopedKey<T>::set
  11: tokio::runtime::scheduler::current_thread::CoreGuard::enter
  12: tokio::runtime::scheduler::current_thread::CoreGuard::block_on
  13: tokio::runtime::scheduler::current_thread::CurrentThread::block_on
  14: tokio::runtime::runtime::Runtime::block_on
  15: rust_out::main
  16: core::ops::function::FnOnce::call_once
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.



failures:
    src/task.rs - task::TaskMetrics::mean_scheduled_duration (line 1924)
    src/task.rs - task::TaskMetrics::total_scheduled_duration (line 922)

test result: FAILED. 56 passed; 2 failed; 2 ignored; 0 measured; 0 filtered out; finished in 35.93s

[jswrenn]

Fixed in #39.