Upgrade System.Memory to 4.6.0 (#15353)

Co-authored-by: Viktor Hofer <[email protected]>

Author: mthalman

eng/Versions.props

@@ -18,7 +18,8 @@
     <SystemCommandLineVersion>2.0.0-beta4.24126.1</SystemCommandLineVersion>
     <!-- corefx -->
     <MicrosoftBclHashCodeVersion>1.1.1</MicrosoftBclHashCodeVersion>
-    <SystemMemoryVersion>4.5.5</SystemMemoryVersion>
+    <SystemMemoryVersion Condition="'$(DotNetBuildSourceOnly)' != 'true'">4.5.5</SystemMemoryVersion>
+    <SystemMemoryVersion Condition="'$(DotNetBuildSourceOnly)' == 'true'">4.6.0</SystemMemoryVersion>
     <SystemRuntimeInteropServicesRuntimeInformation>4.3.0</SystemRuntimeInteropServicesRuntimeInformation>
     <!-- deployment-tools -->
     <MicrosoftDeploymentDotNetReleasesVersion>2.0.0-preview.1.24305.1</MicrosoftDeploymentDotNetReleasesVersion>