Docs: fix GaLore optimizer code example (huggingface#32249)

Docs: fix GaLore optimizer example

Fix incorrect usage of GaLore optimizer in Transformers trainer code example.

The GaLore optimizer uses low-rank gradient updates to reduce memory usage. GaLore is quite popular and is implemented by the authors in [https://github.com/jiaweizzhao/GaLore](https://github.com/jiaweizzhao/GaLore). A few months ago GaLore was added to the HuggingFace Transformers library in huggingface#29588.

Documentation of the Trainer module includes a few code examples of how to use GaLore. However, the `optim_targe_modules` argument to the `TrainingArguments` function is incorrect, as discussed in huggingface#29588 (comment). This pull request fixes this issue.

docs/source/en/trainer.md

@@ -278,7 +278,7 @@ args = TrainingArguments(
     max_steps=100,
     per_device_train_batch_size=2,
     optim="galore_adamw",
-    optim_target_modules=["attn", "mlp"]
+    optim_target_modules=[r".*.attn.*", r".*.mlp.*"]
 )
 
 model_id = "google/gemma-2b"
@@ -315,7 +315,7 @@ args = TrainingArguments(
     max_steps=100,
     per_device_train_batch_size=2,
     optim="galore_adamw",
-    optim_target_modules=["attn", "mlp"],
+    optim_target_modules=[r".*.attn.*", r".*.mlp.*"],
     optim_args="rank=64, update_proj_gap=100, scale=0.10",
 )
 
@@ -359,7 +359,7 @@ args = TrainingArguments(
     max_steps=100,
     per_device_train_batch_size=2,
     optim="galore_adamw_layerwise",
-    optim_target_modules=["attn", "mlp"]
+    optim_target_modules=[r".*.attn.*", r".*.mlp.*"]
 )
 
 model_id = "google/gemma-2b"