Fix TFM inconsistency in BuildHost (#76354)

Author: jjonescz

eng/targets/TargetFrameworks.props

@@ -55,7 +55,7 @@
         <NetRoslyn>$(NetCurrent)</NetRoslyn>
         <NetRoslynSourceBuild>$(NetCurrent);$(NetPrevious)</NetRoslynSourceBuild>
         <NetRoslynAll>$(NetCurrent);$(NetPrevious)</NetRoslynAll>
-        <NetRoslynBuildHostNetCoreVersion>$(NetCurrent)</NetRoslynBuildHostNetCoreVersion>
+        <NetRoslynBuildHostNetCoreVersion>$(NetPrevious)</NetRoslynBuildHostNetCoreVersion>
         <NetRoslynNext>$(NetCurrent)</NetRoslynNext>
       </PropertyGroup>
     </When>