[github-actions] enable Avahi in OTBR CI tests (#6710)

.github/workflows/otbr.yml

@@ -103,6 +103,9 @@ jobs:
 
   thread-border-router:
     runs-on: ubuntu-20.04
+    strategy:
+      matrix:
+        otbr_mdns: ["mDNSResponder", "avahi"]
     env:
       REFERENCE_DEVICE: 1
       VIRTUAL_TIME: 0
@@ -111,6 +114,7 @@ jobs:
       INTER_OP: 1
       COVERAGE: 1
       MULTIPLY: 1
+      OTBR_MDNS: ${{ matrix.otbr_mdns }}
       PYTHONUNBUFFERED: 1
       VERBOSE: 1
       BORDER_ROUTING: 1

script/test

@@ -293,6 +293,7 @@ do_build_otbr_docker()
             --build-arg NAT64=0 \
             --build-arg REST_API=0 \
             --build-arg WEB_GUI=0 \
+            --build-arg MDNS="${OTBR_MDNS:-mDNSResponder}" \
             --build-arg OTBR_OPTIONS="${otbr_options[*]}"
     )