Return value from PeriodicTimer.WaitForNextTickAsync is not properly documented

### Type of issue

Missing information

### Description

`PeriodicTimer.WaitForNextTickAsync` returns `ValueTask`

The documentation for the return describes the `ValueTask` bit of this, but not the meaning of the `bool` contents.

The documentation should cover _both_ the circumstances of the task complation _and_ the value of the result. Currently it only does the former.

### Page URL

https://learn.microsoft.com/en-us/dotnet/api/system.threading.periodictimer.waitfornexttickasync?view=net-10.0

### Content source URL

https://github.com/dotnet/dotnet-api-docs/blob/main/xml/System.Threading/PeriodicTimer.xml

### Document Version Independent Id

0ef31de4-0c6b-4ae5-b172-c2e89beee4cc

### Platform Id

cdfefd6d-f8e5-d855-490d-211d69650a39

### Article author

@dotnet-bot