openai[patch]: upgrade tiktoken and fix test (#30621)

Related to https://github.com/langchain-ai/langchain/issues/30344

https://github.com/langchain-ai/langchain/pull/30542 introduced an
erroneous test for token counts for o-series models. tiktoken==0.8 does
not support o-series models in
`tiktoken.encoding_for_model(model_name)`, and this is the version of
tiktoken we had in the lock file. So we would default to `cl100k_base`
for o-series, which is the wrong encoding model. The test tested against
this wrong encoding (so it passed with tiktoken 0.8).

Here we update tiktoken to 0.9 in the lock file, and fix the expected
counts in the test. Verified that we are pulling
[o200k_base](https://github.com/openai/tiktoken/blob/main/tiktoken/model.py#L8),
as expected.

libs/partners/openai/tests/unit_tests/test_token_counts.py

@@ -10,8 +10,8 @@ _EXPECTED_NUM_TOKENS = {
     "gpt-4": 12,
     "gpt-4-32k": 12,
     "gpt-3.5-turbo": 12,
-    "o1": 12,
-    "o3": 12,
+    "o1": 11,
+    "o3": 11,
     "gpt-4o": 11,
 }