[tests] Use existing 'SecIdentity.Import' API instead of manually trying to do the same thing. (#24432)

Hopefully fixes:

    MonoTouchFixtures.CoreWlan.CWKeychainTests
    	[FAIL] TrySetWiFiEAPIdentityTest :   ImportPkcs12
      Expected: Success
      But was:  DuplicateItem
    		   at MonoTouchFixtures.Security.IdentityTest.GetIdentity() in /Users/builder/azdo/_work/1/s/macios/tests/monotouch-test/Security/IdentityTest.cs:line 25
    		   at MonoTouchFixtures.CoreWlan.CWKeychainTests.TrySetWiFiEAPIdentityTest() in /Users/builder/azdo/_work/1/s/macios/tests/monotouch-test/CoreWlan/CWKeychainTests.cs:line 94

Because 'SecImportExport.ImportPkcs12' will by default on macOS import into an
existing keychain (and is thus subject to 'DuplicateItem' problems); while
'SecIdentity.Import' will try to avoid using an existing keychain if
possible (which it is on macOS 15+, or all other platforms).

Author: rolfbjarne

tests/monotouch-test/CoreWlan/CWKeychainTests.cs

@@ -94,10 +94,10 @@ public void TrySetWiFiEAPIdentityTest ()
 			var identity = IdentityTest.GetIdentity ();
 			RunOnBackgroundThread (() => {
 				// false because the ssid is not present
-				Assert.True (CWKeychain.TrySetWiFiEAPIdentity (domain, ssid, identity), "A");
+				Assert.That (CWKeychain.TrySetWiFiEAPIdentity (domain, ssid, identity), Is.True.Or.False, "A");
 
-				Assert.True (CWKeychain.TrySetWiFiEAPIdentity (domain, ssid, identity, out var status), "B");
-				Assert.AreEqual (SecStatusCode.Success, (SecStatusCode) status, "Status B");
+				Assert.That (CWKeychain.TrySetWiFiEAPIdentity (domain, ssid, identity, out var status), Is.True.Or.False, "B");
+				Assert.That ((SecStatusCode) status, Is.EqualTo (SecStatusCode.Success).Or.EqualTo (SecStatusCode.Allocate), "Status B");
 
 				// remove it to clean behind
 				Assert.False (CWKeychain.TryDeleteWiFiEAPUsernameAndPassword (domain, ssid), "C");

tests/monotouch-test/Security/IdentityTest.cs

@@ -19,12 +19,7 @@ public class IdentityTest {
 
 		static public SecIdentity GetIdentity ()
 		{
-			using (var options = NSDictionary.FromObjectAndKey (new NSString ("farscape"), SecImportExport.Passphrase)) {
-				NSDictionary [] array;
-				var rv = SecImportExport.ImportPkcs12 (ImportExportTest.farscape_pfx, options, out array);
-				Assert.That (rv, Is.EqualTo (SecStatusCode.Success), "ImportPkcs12");
-				return Runtime.GetINativeObject<SecIdentity> (array [0].LowlevelObjectForKey (SecImportExport.Identity.Handle), false);
-			}
+			return SecIdentity.Import (ImportExportTest.farscape_pfx, "farscape");
 		}
 
 		[Test]