Memory leak when using GrainCancellationToken

We use Orleans 3.6.0. Memory leak also is reproducing in 3.6.5

We encountered a memory leak while using `GrainCancellationTokenSource` when single long-running `GrainCancellationToken` was passed at many Grains.

After some research we found that GrainCancellationToken work on `CancellationSourcesExtension`. This extension creates for every Grain where GrainCancellationToken passed to method.

`CancellationSourcesExtension` uses `Interner` which holds `WeakRerences` to all `GrainCancellationToken`. `Interner` has a `System.Threading.Timer` that clears dictionary. This timer references to `Interner` instance by callback method.

`Interner` implements `IDisposable`. His dispose method stops Timer. But `CancellationSourcesExtension` never calls it.

**`CancellationSourcesExtension` is cleaned up by the garbage collector:**


**But `Interner` and its `Timer` not:**

**This is object hierarch:**

P.S. We check source code of this classes at 3.6.5 and do not found any changes.