[tests] Fix BundleStructure when building for only tvOS. (xamarin#20677)

Fix BundleStructure when building for only tvOS by detecting whether the
bindings are zipped or not by detecting the presence of the zip file, instead
of computing it based on the current platform (which becomes problematic,
because whether or not a binding project produces a zip file may depend on
whether other platforms are enabled or not).

tests/dotnet/UnitTests/BundleStructureTest.cs

@@ -646,15 +646,16 @@ public void Build (ApplePlatform platform, string runtimeIdentifiers, CodeSignat
 				expectedWarnings.AddRange (expectedWarnings);
 			}
 
-			var zippedFrameworks = true; //platform == ApplePlatform.MacCatalyst || platform == ApplePlatform.MacOSX;
 			var xcArch = GetXCFrameworkArchitectures (platform, runtimeIdentifiers);
 			foreach (var rid in rids) {
+				var zip = Path.Combine (testsDirectory, "bindings-xcframework-test", "dotnet", platformString, "bin", configuration, tfm, "bindings-framework-test.resources.zip");
+				var zippedFrameworks = File.Exists (zip);
 				if (zippedFrameworks) {
 					expectedWarnings.Add ($"The framework {Path.Combine ("obj", configuration, tfm, rid, "bindings-framework-test.resources.zip", "XStaticObjectTest.xcframework", xcArch, "XStaticObjectTest.framework")} is a framework of static libraries, and will not be copied to the app.");
 					expectedWarnings.Add ($"The framework {Path.Combine ("obj", configuration, tfm, rid, "bindings-framework-test.resources.zip", "XStaticArTest.xcframework", xcArch, "XStaticArTest.framework")} is a framework of static libraries, and will not be copied to the app.");
 				} else {
-					expectedWarnings.Add ($"The framework {Path.Combine (testsDirectory, "bindings-framework-test", "dotnet", platformString, "bin", configuration, tfm, "bindings-framework-test.resources", "XStaticObjectTest.xcframework", xcArch, "XStaticObjectTest.framework")} is a framework of static libraries, and will not be copied to the app.");
-					expectedWarnings.Add ($"The framework {Path.Combine (testsDirectory, "bindings-framework-test", "dotnet", platformString, "bin", configuration, tfm, "bindings-framework-test.resources", "XStaticArTest.xcframework", xcArch, "XStaticArTest.framework")} is a framework of static libraries, and will not be copied to the app.");
+					expectedWarnings.Add ($"The framework {Path.Combine (testsDirectory, "bindings-xcframework-test", "dotnet", platformString, "bin", configuration, tfm, "bindings-framework-test.resources", "XStaticObjectTest.xcframework", xcArch, "XStaticObjectTest.framework")} is a framework of static libraries, and will not be copied to the app.");
+					expectedWarnings.Add ($"The framework {Path.Combine (testsDirectory, "bindings-xcframework-test", "dotnet", platformString, "bin", configuration, tfm, "bindings-framework-test.resources", "XStaticArTest.xcframework", xcArch, "XStaticArTest.framework")} is a framework of static libraries, and will not be copied to the app.");
 				}
 			}