[CI] Fix mypy check in CI (#1655)

### What this PR does / why we need it?
Fix mypy check in CI:
https://github.com/vllm-project/vllm-ascend/actions/runs/16115919385/job/45469646509?pr=1654

Mypy failed due to the greater numpy version. We need to pin
`numpy=1.26.4` in vllm-ascend

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

### How was this patch tested?
CI passed

Signed-off-by: MengqingCao <cmq0113@163.com>

Author: MengqingCao

.github/workflows/vllm_ascend_test.yaml

@@ -103,10 +103,6 @@ jobs:
           pip install yapf==0.32.0
           yapf --diff --recursive .
 
-      - name: Install dependencies
-        run: |
-          pip install -r requirements-dev.txt --extra-index-url https://download.pytorch.org/whl/cpu
-
       - name: Checkout vllm-project/vllm repo
         uses: actions/checkout@v4
         with:
@@ -126,6 +122,10 @@ jobs:
           pip install -r requirements/build.txt --extra-index-url https://download.pytorch.org/whl/cpu
           VLLM_TARGET_DEVICE=empty pip install .
 
+      - name: Install dependencies
+        run: |
+          pip install -r requirements-dev.txt --extra-index-url https://download.pytorch.org/whl/cpu
+
       - name: Mypy Check
         run: |
           echo "::add-matcher::.github/workflows/matchers/mypy.json"