[CI] ensure pyyaml is installed into the correct Python environment (vllm-project#11328)

### What this PR does / why we need it?
- The resolve_nightly_tests.py script requires pyyaml but it was not
pre-installed in the runner container, causing ModuleNotFoundError.
- Added explicit pip3 install step in the authorize job.
- Removed --user flag from the script's fallback install to avoid
PYTHONPATH issues in root containers.

- vLLM version: v0.23.0
- vLLM main:
vllm-project/vllm@a30addc

Signed-off-by: hfadzxy <starmoon_zhang@163.com>

Author: zhangxinyuehfad

.github/workflows/pr_nightly_command.yml

@@ -100,6 +100,10 @@ jobs:
         if: steps.auth.outputs.is_authorized == 'false'
         run: exit 1
 
+      - name: Install Python dependencies
+        if: steps.auth.outputs.is_authorized == 'true'
+        run: pip3 install pyyaml -q
+
       - name: Resolve test cases and branch
         id: resolve
         if: steps.auth.outputs.is_authorized == 'true'

.github/workflows/scripts/resolve_nightly_tests.py

@@ -7,7 +7,7 @@
 try:
     import yaml
 except ImportError:
-    subprocess.check_call(["pip3", "install", "pyyaml", "-q", "--user"])
+    subprocess.check_call(["pip3", "install", "pyyaml", "-q"])
     import yaml