[nat64] run nat64 ci tests as an independent job (#7885)

This commit changes the NAT64 CI tests to be ran as an independent
job. A new /nat64 folder is added and it would make it easier to
configure new NAT64 tests in the future.

.github/workflows/otbr.yml

@@ -113,31 +113,43 @@ jobs:
             otbr_trel: 0
             cert_scripts: ./tests/scripts/thread-cert/border_router/*.py
             packet_verification: 1
+            nat64: 0
             description: ""
           - otbr_mdns: "mDNSResponder"
             otbr_trel: 1
             cert_scripts: ./tests/scripts/thread-cert/border_router/*.py
             packet_verification: 2
+            nat64: 0
             description: ""
           - otbr_mdns: "mDNSResponder"
             otbr_trel: 0
             cert_scripts: ./tests/scripts/thread-cert/border_router/MATN/*.py
             packet_verification: 1
+            nat64: 0
             description: "MATN"
           - otbr_mdns: "mDNSResponder"
             otbr_trel: 0
             cert_scripts: ./tests/scripts/thread-cert/border_router/LowPower/*.py
             packet_verification: 1
+            nat64: 0
             description: "LowPower"
+          - otbr_mdns: "mDNSResponder"
+            otbr_trel: 0
+            cert_scripts: ./tests/scripts/thread-cert/border_router/nat64/*.py
+            packet_verification: 1
+            nat64: 1
+            description: "nat64"
           - otbr_mdns: "avahi"
             otbr_trel: 0
             cert_scripts: ./tests/scripts/thread-cert/border_router/*.py
             packet_verification: 1
+            nat64: 0
             description: ""
           - otbr_mdns: "avahi"
             otbr_trel: 1
             cert_scripts: ./tests/scripts/thread-cert/border_router/*.py
             packet_verification: 2
+            nat64: 0
             description: ""
     name: BR ${{ matrix.description }} (${{ matrix.otbr_mdns }}, TREL=${{matrix.otbr_trel}})
     env:
@@ -152,6 +164,7 @@ jobs:
       PYTHONUNBUFFERED: 1
       VERBOSE: 1
       BORDER_ROUTING: 1
+      NAT64: ${{ matrix.nat64 }}
       MAX_JOBS: 3
     steps:
     - uses: actions/checkout@v2

script/test

@@ -324,7 +324,7 @@ do_build_otbr_docker()
             --build-arg BACKBONE_ROUTER=1 \
             --build-arg REFERENCE_DEVICE=1 \
             --build-arg OT_BACKBONE_CI=1 \
-            --build-arg NAT64=0 \
+            --build-arg NAT64="${NAT64:-0}" \
             --build-arg REST_API=0 \
             --build-arg WEB_GUI=0 \
             --build-arg MDNS="${OTBR_MDNS:-mDNSResponder}" \