Revert commit 142a159 to support python docker 5

Debian bookworm (current stable) still has python3-docker 5.0.3. The
reverted commit prevented the test-suite to run natively on this distro.

The version check could be bumped again when the next Debian stable (trixie)
will be released (by fall 2025 hopefully).

test/conftest.py

@@ -616,5 +616,5 @@ try:
 except docker.errors.ImageNotFound:
     pytest.exit("The docker image 'nginxproxy/nginx-proxy:test' is missing")
 
-if Version(docker.__version__) < Version("7.0.0"):
-    pytest.exit("This test suite is meant to work with the python docker module v7.0.0 or later")
+if Version(docker.__version__) < Version("5.0.0"):
+    pytest.exit("This test suite is meant to work with the python docker module v5.0.0 or later")