Update source-build-externals to latest

Author: MichaelSimons

eng/Version.Details.xml

@@ -500,9 +500,9 @@
       <SourceBuild RepoName="command-line-api" ManagedOnly="true" />
     </Dependency>
     <!-- Intermediate is necessary for source build. -->
-    <Dependency Name="Microsoft.SourceBuild.Intermediate.source-build-externals" Version="10.0.618101">
+    <Dependency Name="Microsoft.SourceBuild.Intermediate.source-build-externals" Version="10.0.620205">
       <Uri>https://github.com/dotnet/source-build-externals</Uri>
-      <Sha>e862af6a41a678bcec164c751c2a3f7a648776cd</Sha>
+      <Sha>b22cfa235a532fd7e371251830f37ca024dc2112</Sha>
       <SourceBuild RepoName="source-build-externals" ManagedOnly="true" />
     </Dependency>
     <!-- Intermediate is necessary for source build. -->