Update Directory.Build.props to explicitly state Version 0.13 (#2194)

## Why make this change?

- For our next rc, bumping to version 0.13 to align with the release
branch that I'll create.

src/Directory.Build.props

@@ -2,7 +2,7 @@
   <PropertyGroup>
     <Nullable>enable</Nullable>
     <BaseOutputPath>..\out</BaseOutputPath>
-    <Version>0.12</Version>
+    <Version>0.13</Version>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">