nonisolated(unsafe) is available only in Swift 5.10 and later

Author: kateinoigakukun

Sources/JavaScriptKit/FundamentalObjects/JSObject.swift

@@ -141,7 +141,9 @@ public class JSObject: Equatable {
 
     // `JSObject` storage itself is immutable, and use of `JSObject.global` from other
     // threads maintains the same semantics as `globalThis` in JavaScript.
+    #if compiler(>=5.10)
     nonisolated(unsafe)
+    #endif
     static let _global = JSObject(id: _JS_Predef_Value_Global)
     #else
     static let _global = JSObject(id: _JS_Predef_Value_Global)