[9.3] Update Elastic.Transport to 0.15.0 (#8830) (#8832)

Co-authored-by: Florian Bernd <git@flobernd.de>

Author: github-actions[bot]

src/Elastic.Clients.Elasticsearch/Elastic.Clients.Elasticsearch.csproj

@@ -31,7 +31,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Elastic.Transport" Version="0.10.3" />
+    <PackageReference Include="Elastic.Transport" Version="0.15.0" />
     <PackageReference Include="PolySharp" Version="1.15.0">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>