Test on HAProxy 2.6

Author: TimWolla

.github/workflows/test.yml

@@ -44,6 +44,7 @@ jobs:
         - "2.3"
         - "2.4"
         - "2.5"
+        - "2.6"
       fail-fast: false
     steps:
     - name: Install HAProxy ${{ matrix.haproxy-versions }}.