Corrected URL path to access the Kaggle Gemma model weights dir (#526)

I have corrected incorrect URL for accessing the Kaggle Gemma-2 model checkpoint and weight directory from "google/gemma-2-2b/pyTorch/gemma-2-{VARIANT}" to "google/gemma-2/pyTorch/gemma-2-{VARIANT}". 

I have updated the URL after verifying on the Kaggle platform and also have successfully implemented and tested in a Colab environment. 

Please find the replicated [gist](https://colab.sandbox.google.com/gist/RenuPatelGoogle/711a744401b32b30048c2f100d0ab7d2/kaggle_gemma2.ipynb) here for the same.

Author: RenuPatelGoogle

site/en/gemma/docs/pytorch_gemma.ipynb

@@ -186,7 +186,7 @@
         "import kagglehub\n",
         "\n",
         "# Load model weights\n",
-        "weights_dir = kagglehub.model_download(f'google/gemma-2-2b/pyTorch/gemma-2-{VARIANT}')"
+        "weights_dir = kagglehub.model_download(f'google/gemma-2/pyTorch/gemma-2-{VARIANT}')"
       ]
     },
     {