Fix URL in comment for contrastive loss function (#24271)

* Update language_modeling.py

in "class TextDatasetForNextSentencePrediction(Dataset)", double considering "self.tokenizer.num_special_tokens_to_add(pair=True)" 

so, i remove self.block_size, and add parameter for "def create_examples_from_document". like "class LineByLineWithSOPTextDataset" do

* Update language_modeling.py

* Fix URL in comment for contrastive loss function

src/transformers/models/clip/modeling_clip.py

@@ -61,7 +61,7 @@ def _expand_mask(mask: torch.Tensor, dtype: torch.dtype, tgt_len: Optional[int]
 
 
 # contrastive loss function, adapted from
-# https://sachinruk.github.io/blog/pytorch/pytorch%20lightning/loss%20function/gpu/2021/03/07/CLIP.html
+# https://sachinruk.github.io/blog/2021-03-07-clip.html
 def contrastive_loss(logits: torch.Tensor) -> torch.Tensor:
     return nn.functional.cross_entropy(logits, torch.arange(len(logits), device=logits.device))