Fix System.Net.Quick.csproj configurations (#1675)

The Configurations.props file was modified to have $(NetCoreAppCurrent)-Linux and
$(NetCoreAppCurrent)-OSX instead of $(NetCoreAppCurrent)-Unix in a recent PR #427,
but the Configurations in the System.Net.Quic.csproj were not updated accordingly.

src/libraries/System.Net.Quic/src/System.Net.Quic.csproj

@@ -2,7 +2,7 @@
   <PropertyGroup>
     <AssemblyName>System.Net.Quic</AssemblyName>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <Configurations>$(NetCoreAppCurrent)-Unix-Debug;$(NetCoreAppCurrent)-Unix-Release;$(NetCoreAppCurrent)-Windows_NT-Debug;$(NetCoreAppCurrent)-Windows_NT-Release</Configurations>
+    <Configurations>$(NetCoreAppCurrent)-Linux-Debug;$(NetCoreAppCurrent)-Linux-Release;$(NetCoreAppCurrent)-OSX-Debug;$(NetCoreAppCurrent)-OSX-Release;$(NetCoreAppCurrent)-Windows_NT-Debug;$(NetCoreAppCurrent)-Windows_NT-Release</Configurations>
     <EnablePInvokeAnalyzer>false</EnablePInvokeAnalyzer>
   </PropertyGroup>
   <ItemGroup>