Revise `AnalysisLevel` note for correctness

https://github.com/dotnet/sdk/blob/7347d27e2fc7a25de75e00083d379660dca87689/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.Analyzers.targets#L18-L27

It looks like, for .NET 5, the default value is 5.0, but for any newer version, the default is latest.

The documentation says:

> The default value for the AnalysisLevel property is latest, which means you always get the latest code analysis rules as you move to newer versions of the .NET SDK.

which seems to apply only for .NET 6 and greater.

@mavasani Can you confirm?

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#### Document Details

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* ID: f8906b2c-b984-0427-d064-829e7ea2fc55
* Version Independent ID: 128f9903-971d-6a66-a2cb-9b12acbc55e7
* Content: [Code analysis in .NET](https://docs.microsoft.com/en-us/dotnet/fundamentals/code-analysis/overview)
* Content Source: [docs/fundamentals/code-analysis/overview.md](https://github.com/dotnet/docs/blob/main/docs/fundamentals/code-analysis/overview.md)
* Product: **dotnet-fundamentals**
* GitHub Login: @gewarren
* Microsoft Alias: **gewarren**