System.Runtime.Serialization.Formatters: fix target framework check f…

…or source-build. (#104735)

* System.Runtime.Serialization.Formatters: fix target framework check for source-build.

The inbox implementation should no longer include a working binary formatter.

The check used to build a working formatter was '$(TargetFramework)' == '$(NetCoreAppMinimum)'.

Because NetCoreAppMinimum gets set to TargetFramework in the source-build configuration,
the source-build configuration unintentionally included a working binary formatter.

* Don't build the net8.0 target when DotNetBuildSourceOnly.

* Join lines.

src/libraries/System.Runtime.Serialization.Formatters/src/System.Runtime.Serialization.Formatters.csproj

@@ -12,7 +12,7 @@
   <PropertyGroup>
     <NoWarn>$(NoWarn);CA1822;IDE0060</NoWarn>
 
-    <FunctioningBinaryFormatter Condition="'$(TargetFramework)' == '$(NetCoreAppMinimum)'">true</FunctioningBinaryFormatter>
+    <FunctioningBinaryFormatter Condition="'$(TargetFramework)' == '$(NetCoreAppMinimum)' and '$(DotNetBuildSourceOnly)' != 'true'">true</FunctioningBinaryFormatter>
     <!-- The GenerateNuspec target fails if this property is keyed off of FunctioningBinaryFormatter, so keep it logically in sync --> 
     <IncludeBuildOutput Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">false</IncludeBuildOutput>
     <SuppressDependenciesWhenPacking Condition="'$(FunctioningBinaryFormatter)' != 'true'">true</SuppressDependenciesWhenPacking>