[PHI] Add missing const qualifier for Tensor.contiguous (#74264)

Author: SigureMo

paddle/phi/api/include/tensor.h

@@ -672,7 +672,7 @@ class PADDLE_API Tensor final {
  *
  * @return Tensor
  */
- Tensor contiguous();
+ Tensor contiguous() const;
 
  private:
  /**

paddle/phi/api/lib/tensor.cc

@@ -549,7 +549,7 @@ bool Tensor::is_contiguous() const {
  }
 }
 
-Tensor Tensor::contiguous() {
+Tensor Tensor::contiguous() const {
  if (is_dense_tensor() || is_dist_tensor()) {
  phi::DenseTensor *dense_tensor = nullptr;
  if (is_dist_tensor()) {