fix: Updating test setup to build webhost

[gavin-aguiar]

Description

After the split host feature, the test setup was getting an error while trying to build the host locally

C:\Nuget\microsoft.azure.webjobs.script.extensionsmetadatagenerator\4.0.1\build\Microsoft.Azure.WebJobs.Script.ExtensionsMetadataGenerator.targets(24,5): error MSB4018: The "RemoveRuntimeDependencies" task failed unexpectedly. [G:\Repos\python\azure-functions-python-worker\build\webhost\test\CSharpPrecompiledTestProjects\WebJobsStartupTests\WebJobsStartupTests.csproj]
C:\Nuget\microsoft.azure.webjobs.script.extensionsmetadatagenerator\4.0.1\build\Microsoft.Azure.WebJobs.Script.ExtensionsMetadataGenerator.targets(24,5): error MSB4018: System.IO.IOException: The process cannot access the file 'G:\Repos\python\azure-functions-python-worker\build\webhost\bin\bin\Microsoft.Azure.WebJobs.dll' because it is being used by another process.

Updated the test setups to disable parallel builds so that the dlls are not locked.

Fixes #

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