Add gemma3 onnxruntime tests

Author: simondanielsson

tests/onnxruntime/testing_utils.py

@@ -67,6 +67,7 @@
     "flaubert": "hf-internal-testing/tiny-random-flaubert",
     "flux": "optimum-internal-testing/tiny-random-flux",
     "gemma": "fxmarty/tiny-random-GemmaForCausalLM",
+    "gemma3": "hf-internal-testing/tiny-random-Gemma3ForConditionalGeneration",
     "gpt2": "hf-internal-testing/tiny-random-GPT2LMHeadModel",
     "gpt_bigcode": "hf-internal-testing/tiny-random-GPTBigCodeModel",
     "gpt_bigcode-multi_query-False": "optimum-internal-testing/tiny-random-gpt_bigcode-multi_query-False",