Prepare release of MSTest 3.6.4 (#4215)

Author: Evangelink

eng/Versions.props

@@ -1,9 +1,9 @@
 <Project>
   <PropertyGroup Label="Version settings">
     <!-- MSTest version -->
-    <VersionPrefix>3.6.3</VersionPrefix>
+    <VersionPrefix>3.6.4</VersionPrefix>
     <!-- Testing Platform version -->
-    <TestingPlatformVersionPrefix>1.4.3</TestingPlatformVersionPrefix>
+    <TestingPlatformVersionPrefix>1.4.4</TestingPlatformVersionPrefix>
     <PreReleaseVersionLabel>preview</PreReleaseVersionLabel>
   </PropertyGroup>
   <PropertyGroup Label="MSTest prod dependencies - darc updated">