[Concurrency] Fix some comments and a typo.

There were a couple of comments that needed updating, and a typo
in a function name.

rdar://141348916

Author: al45tair

stdlib/public/Concurrency/Executor.swift

@@ -592,7 +592,7 @@ extension Task where Success == Never, Failure == Never {
   ///   2. The preferred executor for the currently executing `Task`, or
   ///   3. The task executor for the current thread
   ///
-  ///  If none of these exist, this property will be `nil`.
+  ///  If none of these exist, returns the default executor.
   @available(SwiftStdlib 6.2, *)
   @_unavailableInEmbedded
   public static var currentExecutor: any Executor {

stdlib/public/Concurrency/ExecutorImpl.swift

@@ -33,7 +33,7 @@ internal func drainMainQueue() {
 
 @available(SwiftStdlib 6.2, *)
 @_silgen_name("swift_task_donateThreadToGlobalExecutorUntilImpl")
-internal func dontateToGlobalExecutor(
+internal func donateToGlobalExecutor(
   condition: @convention(c) (_ ctx: UnsafeMutableRawPointer) -> CBool,
   context: UnsafeMutableRawPointer
 ) {

test/Concurrency/Runtime/clocks.swift

@@ -144,7 +144,7 @@ struct TockingClock: Clock {
 
   // These are a bit of a lie, since this clock is weird and doesn't
   // actually tell the time; for the purposes of this test, we pretend
-  // that the tocks are 20ms.
+  // that the tocks are 10ms.
   func convert(from duration: Duration) -> Swift.Duration? {
     return .seconds(Double(duration.tocks) / 100)
   }