Equals vs GetHashCode using GroupBy

Apparently not only the equality function is being called but also the GetHashCode when using GroupBy with
GroupBy<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>).
There isn't anything said about GetHashCode in the documentation.

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* ID: 2bee8281-80cd-8648-6425-d39ef3cfd90a
* Version Independent ID: 9126a563-3b4c-fc7f-60a7-1c19ea26dddb
* Content: [Enumerable.GroupBy Method (System.Linq)](https://docs.microsoft.com/en-us/dotnet/api/system.linq.enumerable.groupby?view=netframework-4.7.2#System_Linq_Enumerable_GroupBy__2_System_Collections_Generic_IEnumerable___0__System_Func___0___1__)
* Content Source: [xml/System.Linq/Enumerable.xml](https://github.com/dotnet/dotnet-api-docs/blob/master/xml/System.Linq/Enumerable.xml)
* Product: **dotnet-api**
* GitHub Login: @dotnet-bot
* Microsoft Alias: **dotnetcontent**