Add optional parameter to FlutterTesterDevices. (#158133)

This is to handle Google testing failures for  https://github.com/flutter/flutter/pull/158126.

We want to update G3 to provide this parameter before merging the full change.

Testing is not needed because the change is no-op.

packages/flutter_tools/lib/src/tester/flutter_tester.dart

@@ -266,6 +266,8 @@ class FlutterTesterDevices extends PollingDeviceDiscovery {
     required Logger logger,
     required FlutterVersion flutterVersion,
     TestCompilerNativeAssetsBuilder? nativeAssetsBuilder,
+    // ignore: avoid_unused_constructor_parameters, temporarily unused to prepare G3.
+    bool useImplicitPubspecResolution = true,
   }) : _testerDevice = FlutterTesterDevice(
         kTesterDeviceId,
         fileSystem: fileSystem,