Update project.pbxproj to pin to 0.6.0 (#11)

Author: shoumikhin

apple/ExecuTorchDemo/ExecuTorchDemo.xcodeproj/project.pbxproj

@@ -806,7 +806,7 @@
 			isa = XCRemoteSwiftPackageReference;
 			repositoryURL = "https://github.com/pytorch/executorch";
 			requirement = {
-				branch = "swiftpm-0.7.0.20250401";
+				branch = "swiftpm-0.6.0";
 				kind = branch;
 			};
 		};