Add .NET 9 support

Author: nkolev92

TrustTestCert/Program.cs

@@ -69,7 +69,11 @@ private static int MainCore(string[] args)
                 {
                     case "-c":
                     case "--certificate":
+#if NET9_0_OR_GREATER
+                        certificate = X509CertificateLoader.LoadCertificateFromFile(nextArg);
+#else
                         certificate = new X509Certificate2(nextArg);
+#endif
                         break;
 
                     case "-csl":

TrustTestCert/TrustTestCert.csproj

@@ -2,7 +2,7 @@
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <AssemblyName>TrustTestCert</AssemblyName>
-    <TargetFrameworks>net6.0;net7.0;net8.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;net7.0;net8.0;net9.0</TargetFrameworks>
     <Deterministic>true</Deterministic>
     <Features>strict</Features>
     <LangVersion>preview</LangVersion>