Update the SDK to 6.0 Preview 3

[ViktorHofer]

Updating the minimum and target version of the SDK to 6.0 Preview 3.

Contributes to #51716

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Issue Details

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Updating the minimum and target version of the SDK to 6.0 Preview 3.

Contributes to #51716

Author:	ViktorHofer
Assignees:	ViktorHofer
Labels:	area-Infrastructure
Milestone:	6.0.0

[eerhardt]

@joperezr - can you look into unblocking the dotnet-linker-tests?

[joperezr]

Sure taking a look

[joperezr]

linker tests are passing locally after that change I just pushed, so hopefully that will be enough for merging.

TL;DR for those interested, the new SDK has now a)Enabled a linker roslyn analyzer by default which was throwing some errors and b) it changed some defaults of when linker warnings are suppressed. My latest commit will just disable the analyzer for our tests and re-add the trimming warning suppressions we had before the sdk bump.

[eerhardt]

The trimming tests changes look fine to me.

[ViktorHofer]

@joperezr @eerhardt can you please also look at the remaining linker warnings from the other failing legs?

[eerhardt]

 error IL2009: (NETCORE_ENGINEERING_TELEMETRY=Build) Could not find method 'ApplyUpdateSdb' on type 'System.Reflection.Metadata.AssemblyExtensions'

Looks like we have a dangling reference to a method that was removed in #51954. I'll remove the entry in the ILLink.Descriptors.xml file.

fyi @lambdageek

[ViktorHofer]

Failure is #11063
The timeout is due to the product build taking 105 minutes which is unacceptable. Likely because of a slow machine again.