Fix vstest analyzer errors

[mthalman]

Ignores the following analyzer errors when attempting to run a bootstrap stage 2 build:

/repos/dotnet/src/vstest/artifacts/source-build/self/src/src/Microsoft.TestPlatform.AdapterUtilities/ManagedNameUtilities/InvalidManagedNameException.cs(14,93): error SYSLIB0051: 'Exception.Exception(SerializationInfo, StreamingContext)' is obsolete: 'This API supports obsolete formatter-based serialization. It should not be called or extended by application code.' (https://aka.ms/dotnet-warnings/SYSLIB0051) [/repos/dotnet/src/vstest/artifacts/source-build/self/src/src/Microsoft.TestPlatform.AdapterUtilities/Microsoft.TestPlatform.AdapterUtilities.csproj::TargetFramework=net8.0]

/repos/dotnet/src/vstest/artifacts/source-build/self/src/src/Microsoft.TestPlatform.Utilities/XmlUtilities.cs(96,65): error IDE0059: Unnecessary assignment of a value to 'childNodeNavigator' (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0059) [/repos/dotnet/src/vstest/artifacts/source-build/self/src/src/Microsoft.TestPlatform.Utilities/Microsoft.TestPlatform.Utilities.csproj::TargetFramework=net8.0]

Related: microsoft/vstest#4424, microsoft/vstest#4425