[WebNN EP] Fix issues of GRU operator (microsoft#22123)

### Description
This PR fixes the spelling of the key value of the GRU operator in the
map in the `GetSupportedNodes` function (Gru -> GRU) and removes the
data type check for the fifth input (sequence_lens) of the GRU operator.

PTAL, thanks!

onnxruntime/core/providers/webnn/builders/impl/gru_op_builder.cc

@@ -26,8 +26,8 @@ class GruOpBuilder : public BaseOpBuilder {
  private:
   bool IsOpSupportedImpl(const InitializedTensorSet& initializers, const Node& node,
                          const WebnnDeviceType /*device_type*/, const logging::Logger& logger) const override;
-  bool HasSupportedInputsImpl(const InitializedTensorSet& /* initializers */, const Node& node,
-                              const emscripten::val& wnn_limits, const logging::Logger& logger) const override;
+  bool HasSupportedInputsImpl(const Node& node, const emscripten::val& wnn_limits,
+                              const logging::Logger& logger) const override;
   bool HasSupportedOutputsImpl(const Node& node, const emscripten::val& wnn_limits,
                                const logging::Logger& logger) const override;
 };