build: use focal in gitian descriptors

Compilers used change as follows:
Linux native GCC 7.5 -> GCC 8.4
Linux cross GCC 8.4 -> GCC 8.4
Windows mingw-w64 7.3 -> mingw-w64 9.3
macOS Clang 8.0.0 -> Clang 8.0.0

The macOS and Win cross builds in the CI are updated to use Focal, and
per the op, running the security tests is disabled in the Windows
build.

ci/test/00_setup_env_win64.sh

@@ -7,11 +7,10 @@
 export LC_ALL=C.UTF-8
 
 export CONTAINER_NAME=ci_win64
-export DOCKER_NAME_TAG=ubuntu:18.04  # Check that bionic can cross-compile to win64 (bionic is used in the gitian build as well)
+export DOCKER_NAME_TAG=ubuntu:20.04  # Check that Focal can cross-compile to win64 (Focal is used in the gitian build as well)
 export HOST=x86_64-w64-mingw32
 export PACKAGES="python3 nsis g++-mingw-w64-x86-64 wine-binfmt wine64 file"
 export RUN_FUNCTIONAL_TESTS=false
-export RUN_SECURITY_TESTS="true"
 export GOAL="deploy"
 export BITCOIN_CONFIG="--enable-reduce-exports --disable-gui-tests --without-boost-process"