Update ffi gem installation instructions (#103008)

packages/flutter_tools/lib/src/macos/cocoapods.dart

@@ -371,7 +371,7 @@ class CocoaPods {
       ).send();
       _logger.printError(
         'Error: To set up CocoaPods for ARM macOS, run:\n'
-        '  arch -x86_64 sudo gem install ffi\n',
+        '  sudo gem uninstall ffi && sudo gem install ffi -- --enable-libffi-alloc\n',
         emphasis: true,
       );
     }

packages/flutter_tools/test/general.shard/macos/cocoapods_test.dart

@@ -536,6 +536,10 @@ Note: as of CocoaPods 1.0, `pod repo update` does not happen on `pod install` by
           logger.errorText,
           contains('set up CocoaPods for ARM macOS'),
         );
+        expect(
+          logger.errorText,
+          contains('enable-libffi-alloc'),
+        );
         expect(usage.events, contains(const TestUsageEvent('pod-install-failure', 'arm-ffi')));
       });
     });