fix(ci): pin DOCKER_API_VERSION=1.43 for Testcontainers on NAS runner

Testcontainers 2.0.2 (via Spring Boot 4.0) negotiates Docker API 1.44,
but the NAS runner has Docker Engine 24.x which caps at 1.43. Forcing
the client version down unblocks tests until Docker is upgraded on the NAS.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -52,6 +52,8 @@ jobs:
   backend-unit-tests:
     name: Backend Unit Tests
     runs-on: ubuntu-latest
+    env:
+      DOCKER_API_VERSION: "1.43"  # NAS runner runs Docker 24.x (max API 1.43); Testcontainers 2.x defaults to 1.44
     steps:
       - uses: actions/checkout@v4