Add to changelog for Microsoft.Azure.ServiceBus SDK version 5.1.2

[DorothySun216]

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[jsquire]

Are we running API Compat on T1 libraries? If so, this should stay.

//cc: @JoshLove-msft, do you know for sure?

[JoshLove-msft]

I'm not sure, but this would get added automatically after release to reference the new version.

[JoshLove-msft]

But ideally, we wouldn't touch the ApiCompatVersion as it should be handled automatically.

[JoshLove-msft]

Please revert the ApiCompatVersion deletion and then we should be good to merge.

[JoshLove-msft]

/cc @weshaggard do you know if ApiCompat is run for T1 libraries? For Service Bus T1 in particular, they use a test to detect API changes.

[JoshLove-msft]

#18995

[weshaggard]

Yes ApiCompat should be run on any library that is participating in our engineering system.