CI: reduce ASAN log redirection umbrella size

previously ASAN_OPTIONS=log_path=asan.log was intended for VTest
execution only, it should not affect "haproxy -vv" and hsproxy
config smoke testing

.github/workflows/vtest.yml

@@ -42,8 +42,6 @@ jobs:
       # Configure a short TMPDIR to prevent failures due to long unix socket
       # paths.
       TMPDIR: /tmp
-      # Force ASAN output into asan.log to make the output more readable.
-      ASAN_OPTIONS: log_path=asan.log
       OT_CPP_VERSION: 1.6.0
     steps:
     - uses: actions/checkout@v4
@@ -143,6 +141,9 @@ jobs:
       run: echo "::add-matcher::.github/vtest.json"
     - name: Run VTest for HAProxy ${{ steps.show-version.outputs.version }}
       id: vtest
+      env:
+        # Force ASAN output into asan.log to make the output more readable.
+        ASAN_OPTIONS: log_path=asan.log
       run: |
         # This is required for macOS which does not actually allow to increase
         # the '-n' soft limit to the hard limit, thus failing to run.