Make Gemma and Gemma 2 accept inputs_embeds like Gemma 3 (#36787)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

tests/basic_correctness/test_basic_correctness.py

@@ -11,6 +11,8 @@ from unittest.mock import Mock
 
 import pytest
 import torch
+from packaging.version import Version
+from transformers import __version__ as TRANSFORMERS_VERSION
 
 from vllm import LLM
 from vllm.platforms import current_platform
@@ -91,6 +93,15 @@ def test_models(
         if enable_prompt_embeds:
             with torch.no_grad():
                 prompt_embeds = hf_model.get_prompt_embeddings(example_prompts)
+            if model == "hmellor/tiny-random-Gemma2ForCausalLM" and (
+                Version(TRANSFORMERS_VERSION) < Version("5.3.0.dev0")
+            ):
+                # For Gemma 1/2 models with Transformers 5.4.0+, the prompt embeddings
+                # are normalised in `get_prompt_embeddings`, like Gemma 3.
+                # For older versions, we need to manually normalise.
+                embed_scale = hf_model.config.hidden_size**0.5
+                normalizer = torch.tensor(embed_scale, dtype=prompt_embeds[0].dtype)
+                prompt_embeds = [p_e * normalizer for p_e in prompt_embeds]
 
     with VllmRunner(
         model,