Test on HAProxy 2.9

Author: TimWolla

.github/workflows/test.yml

@@ -47,6 +47,7 @@ jobs:
         - "2.6"
         - "2.7"
         - "2.8"
+        - "2.9"
       fail-fast: false
     steps:
     - name: Install HAProxy ${{ matrix.haproxy-versions }}.