fix: use FoundationNetworking

Author: kalinjul

modules/openapi-generator/src/main/resources/swift5/api.mustache

@@ -5,10 +5,10 @@
 // https://openapi-generator.tech
 //
 
-import Foundation{{#usePromiseKit}}
+import Foundation
 #if canImport(FoundationNetworking)
 import FoundationNetworking
-#endif
+#endif{{#usePromiseKit}}
 import PromiseKit{{/usePromiseKit}}{{#useRxSwift}}
 import RxSwift{{/useRxSwift}}{{#useCombine}}
 #if canImport(Combine)