minor optimization: move creation of X509 Subject Summary into catch block on MacOS. (#54774)

src/libraries/System.Security.Cryptography.X509Certificates/src/Internal/Cryptography/Pal.OSX/AppleCertificatePal.cs

@@ -399,7 +399,6 @@ private void EnsureCertData()
                 return;
 
             Debug.Assert(!_certHandle.IsInvalid);
-            string? subjectSummary = Interop.AppleCrypto.X509GetSubjectSummary(_certHandle);
 
             try
             {
@@ -407,6 +406,7 @@ private void EnsureCertData()
             }
             catch (CryptographicException e)
             {
+                string? subjectSummary = Interop.AppleCrypto.X509GetSubjectSummary(_certHandle);
                 if (subjectSummary is null)
                 {
                     throw;