[Test] add test for prefix cache feature of deepseek (#3733)

### What this PR does / why we need it?
This PR adds a prefix cache case for nightly test for
DeepSeek-r1-0528-W8A8 on A3, we need test them daily.

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?
By running the test

- vLLM version: v0.11.0rc3
- vLLM main:
17c540a993

---------

Signed-off-by: root <root@hostname-2pbfv.foreman.pxe>
Co-authored-by: root <root@hostname-2pbfv.foreman.pxe>

.github/workflows/vllm_ascend_test_nightly_a3.yaml

@@ -65,6 +65,9 @@ jobs:
           - name: deepseek-r1-0528-w8a8
             os: linux-aarch64-a3-16
             tests: tests/e2e/nightly/models/test_deepseek_r1_0528_w8a8.py
+          - name: deepseek-r1-0528-w8a8-prefix-cache
+            os: linux-aarch64-a3-16
+            tests: tests/e2e/nightly/features/test_prefix_cache_deepseek_r1_0528_w8a8.py
     uses: ./.github/workflows/_e2e_nightly_single_node.yaml
     with:
       vllm: v0.11.0