Add explicit visionOS deployment target (#3642)

This fixes a compilation error with `Xcode 15.3 beta 2`.

Because we were missing the deployment target, Xcode defaults to the
latest (which is `1.1`), and fails with a deprecation warning.

RevenueCat.xcodeproj/project.pbxproj

@@ -4509,6 +4509,7 @@
 				VERSIONING_SYSTEM = "apple-generic";
 				VERSION_INFO_PREFIX = "";
 				WATCHOS_DEPLOYMENT_TARGET = 6.2;
+				XROS_DEPLOYMENT_TARGET = 1.0;
 			};
 			name = Debug;
 		};
@@ -4573,6 +4574,7 @@
 				VERSIONING_SYSTEM = "apple-generic";
 				VERSION_INFO_PREFIX = "";
 				WATCHOS_DEPLOYMENT_TARGET = 6.2;
+				XROS_DEPLOYMENT_TARGET = 1.0;
 			};
 			name = Release;
 		};