[br-tests] enable BR tests with TREL (#7022)

This commit runs all Border Router (OTBR) tests with TREL enabled.

.github/workflows/otbr.yml

@@ -105,7 +105,14 @@ jobs:
     runs-on: ubuntu-20.04
     strategy:
       matrix:
-        otbr_mdns: ["mDNSResponder", "avahi"]
+        include:
+          - otbr_mdns: "mDNSResponder"
+            otbr_trel: 0
+          - otbr_mdns: "mDNSResponder"
+            otbr_trel: 1
+          - otbr_mdns: "avahi"
+            otbr_trel: 0
+    name: BR (${{ matrix.otbr_mdns }}, TREL=${{matrix.otbr_trel}})
     env:
       REFERENCE_DEVICE: 1
       VIRTUAL_TIME: 0
@@ -123,6 +130,7 @@ jobs:
     - name: Build OTBR Docker
       env:
         GITHUB_TOKEN: "${{ secrets.GITHUB_TOKEN }}"
+        TREL: ${{ matrix.otbr_trel }}
       run: |
         ./script/test build_otbr_docker
     - name: Bootstrap