[v0.18.0][CI] Fix and simplify the CI for Qwen3 32B (#8093)

### What this PR does / why we need it?
This PR fixes and simplifies the CI configuration for Qwen3 32B.

The main changes are:
- Remove the redundant `Qwen3-32B-Int8-A3-Feature-Stack3.yaml` config
and consolidate the CI setup into `Qwen3-32B-Int8.yaml`.
- Improve runtime stability by adding
`PYTORCH_NPU_ALLOC_CONF=expandable_segments:True` and setting
`--max-num-seqs 80`.
- Update the accuracy benchmark from `aime2024` to `gsm8k-lite`, and
adjust the related dataset config, output length, baseline, and
threshold accordingly.

These changes make the Qwen3 32B CI easier to maintain and more stable
in nightly validation.

---------

Signed-off-by: ZYang6263 <zy626375@gmail.com>

.github/workflows/schedule_nightly_test_a3.yaml

@@ -214,9 +214,6 @@ jobs:
           - name: qwen2-5-vl-32b
             os: linux-aarch64-a3-4
             config_file_path: Qwen2.5-VL-32B-Instruct.yaml
-          - name: qwen3-32b-int8-a3-feature-stack3
-            os: linux-aarch64-a3-4
-            config_file_path: Qwen3-32B-Int8-A3-Feature-Stack3.yaml
           - name: qwen3-32b-int8-prefix-cache
             os: linux-aarch64-a3-4
             config_file_path: Prefix-Cache-Qwen3-32B-Int8.yaml