gemma_300m_lora variant is missing in Variant (#555)

fixing this as it will throw an annoying log every time the model is
used.

Author: kvablack

src/openpi/models/gemma.py

@@ -52,7 +52,7 @@ class Config:
     lora_configs: dict[str, lora.LoRAConfig] = dataclasses.field(default_factory=dict)
 
 
-Variant = Literal["dummy", "gemma_300m", "gemma_2b", "gemma_2b_lora"]
+Variant = Literal["dummy", "gemma_300m", "gemma_300m_lora", "gemma_2b", "gemma_2b_lora"]
 
 
 def get_config(variant: Variant) -> Config: