Update dependencies from https://github.com/dotnet/source-build-exter…

…nals build 20240821.1 (#106812)

Microsoft.SourceBuild.Intermediate.source-build-externals
 From Version 9.0.0-alpha.1.24420.1 -> To Version 9.0.0-alpha.1.24421.1

Co-authored-by: dotnet-maestro[bot] <dotnet-maestro[bot]@users.noreply.github.com>
Co-authored-by: Larry Ewing <lewing@microsoft.com>

eng/Version.Details.xml

@@ -81,9 +81,9 @@
       <SourceBuild RepoName="source-build-reference-packages" ManagedOnly="true" />
     </Dependency>
     <!-- Intermediate is necessary for source build. -->
-    <Dependency Name="Microsoft.SourceBuild.Intermediate.source-build-externals" Version="9.0.0-alpha.1.24420.1">
+    <Dependency Name="Microsoft.SourceBuild.Intermediate.source-build-externals" Version="9.0.0-alpha.1.24421.1">
       <Uri>https://github.com/dotnet/source-build-externals</Uri>
-      <Sha>ee22054b44ec9615dc3481c4decc1b007a83a2b0</Sha>
+      <Sha>457ff6ef4705a0aa8de628a1f2a15474a05b7150</Sha>
       <SourceBuild RepoName="source-build-externals" ManagedOnly="true" />
     </Dependency>
   </ProductDependencies>