chore: Reduce flakes in test_text_inference on smaller models (#1428)

# What does this PR do?

When running `tests/integration/inference/test_text_inference.py` on
smaller models, such as Llama-3.2-3B-Instruct, I sometimes get test
flakes where the model passes "San Francisco" as an argument to my tool
call instead of "San Francisco, CA" which is what we expect.

So, this expands upon that tool calling parameter's description to
explicitly state that both city and state are required. With this
change, the tool calling tests that are checking for this "San
Francisco, CA" value are always passing for me instead of sometimes
failing.

## Test Plan

I test this locally via vLLM like:

```
VLLM_URL="http://localhost:8000/v1" \
INFERENCE_MODEL="meta-llama/Llama-3.2-3B-Instruct" \
LLAMA_STACK_CONFIG=remote-vllm \
python -m pytest -v \
tests/integration/inference/test_text_inference.py \
--inference-model "meta-llama/Llama-3.2-3B-Instruct" \
--vision-inference-model ""
```

I don't expect this would negatively impact the parameter generated for
this tool call by other models, as we're providing additional guidance
but not removing any of the existing guidance. However, I cannot easily
confirm that myself.

Signed-off-by: Ben Browning <bbrownin@redhat.com>

tests/integration/test_cases/inference/chat_completion.json

@@ -50,7 +50,7 @@
           "parameters": {
             "location": {
               "param_type": "string",
-              "description": "The city and state, e.g. San Francisco, CA"
+              "description": "The city and state (both required), e.g. San Francisco, CA."
             }
           }
         }