chore(deps): update dotnet monorepo to v7 (major)

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
Microsoft.Extensions.Caching.Memory (source)	nuget	major	6.0.1 -> 7.0.0
System.Composition.AttributedModel (source)	nuget	major	6.0.0 -> 7.0.0
System.Composition.Convention (source)	nuget	major	6.0.0 -> 7.0.0
System.Composition.Hosting (source)	nuget	major	6.0.0 -> 7.0.0
System.Composition.Runtime (source)	nuget	major	6.0.0 -> 7.0.0
System.Composition.TypedParts (source)	nuget	major	6.0.0 -> 7.0.0
System.Threading.Tasks.Dataflow (source)	nuget	major	6.0.0 -> 7.0.0

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[JamieMagee]

Test failure is due to #353