Update dependency log4net to v2.0.15 (#3111)

Author: renovate[bot]

src/NHibernate.Test/NHibernate.Test.csproj

@@ -54,7 +54,7 @@
     </Compile>
   </ItemGroup>
   <ItemGroup>
-    <PackageReference Include="log4net" Version="2.0.14" />
+    <PackageReference Include="log4net" Version="2.0.15" />
     <PackageReference Include="Microsoft.AspNetCore.OData" Version="7.5.12" />
     <PackageReference Include="Microsoft.Data.SqlClient" Version="3.0.0" />
     <PackageReference Include="System.Data.SQLite.Core" Version="1.0.115.5" />