Merge bitcoin/bitcoin#22388: ci: use Ubuntu 20.04 as the default Docker container

7fc1e14 ci: use Ubuntu 20.04 as the default Docker container (fanquake)

Pull request description:

  All but 2 of the Ubuntu CIs (native qt5 & nowallet) are already using 20.04 or 21.04.

ACKs for top commit:
  MarcoFalke:
    cr ACK 7fc1e14

Tree-SHA512: f35d79a87af6c6955695b5e627884f94aed19bafaed4657d03ef4db66cf47cae5311464bb39961570140325652941283b9d88dff862776e8becfff9130162917

Author: MarcoFalke

ci/test/00_setup_env.sh

@@ -47,7 +47,7 @@ export RUN_FUZZ_TESTS=${RUN_FUZZ_TESTS:-false}
 export EXPECTED_TESTS_DURATION_IN_SECONDS=${EXPECTED_TESTS_DURATION_IN_SECONDS:-1000}
 
 export CONTAINER_NAME=${CONTAINER_NAME:-ci_unnamed}
-export DOCKER_NAME_TAG=${DOCKER_NAME_TAG:-ubuntu:18.04}
+export DOCKER_NAME_TAG=${DOCKER_NAME_TAG:-ubuntu:20.04}
 # Randomize test order.
 # See https://www.boost.org/doc/libs/1_71_0/libs/test/doc/html/boost_test/utf_reference/rt_param_reference/random.html
 export BOOST_TEST_RANDOM=${BOOST_TEST_RANDOM:-1}