--source-build switch not recognized in backflow PRs

[ViktorHofer]

Example build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1042199&view=logs&jobId=d9a2c968-0c29-50c0-499a-f355887b82bf&j=d9a2c968-0c29-50c0-499a-f355887b82bf&t=86536739-f147-5c06-fc84-7aaf13bae920

from dotnet/runtime#115545

MSBUILD : error MSB1001: Unknown switch.
    Full command line: '/__w/1/s/.dotnet/sdk/10.0.100-preview.3.25201.16/MSBuild.dll -maxcpucount -verbosity:m -tlp:default=auto /m /nologo /clp:Summary /v:minimal /nr:false /warnaserror /p:TreatWarningsAsErrors=true /p:ContinuousIntegrationBuild=true /__w/1/s/.packages/microsoft.dotnet.arcade.sdk/10.0.0-beta.25263.108/tools/Build.proj /bl:"/__w/1/s/artifacts/log/Release/Build.binlog" /p:Configuration=Release /p:RepoRoot=/__w/1/s/ /p:Restore=true /p:Build=true /p:DotNetBuildRepo=false /p:DotNetBuildSourceOnly=false /p:Rebuild=false /p:Test=false /p:Pack=true /p:IntegrationTest=false /p:PerformanceTest=false /p:Sign=false /p:Publish=false /p:RestoreStaticGraphEnableBinaryLogger=true /p:BuildAllConfigurations=true -tl:false /p:TargetArchitecture=x64 /p:BuildArchitecture=x64 /p:CMakeArgs="" --source-build /p:TargetRid=linux-x64 -logger:/__w/1/s/.packages/microsoft.dotnet.arcade.sdk/10.0.0-beta.25263.108/tools/net/Microsoft.DotNet.ArcadeLogging.dll'
  Switches appended by response files:
Switch: --source-build

Regressed with dotnet/dotnet@d780717