fix .github/workflows/config.yml: cleanup docker bash script of deban-unstable for further commit #302

Job	Run time
osx	5m 28s
debian-unstale (amd64/debian:unstable-slim, amd64, Linux64)	1m 13s
debian-unstale (arm32v7/debian:unstable-slim, arm, LinuxARM)	1m 4s
debian-unstale (arm64v8/debian:unstable-slim, aarch64, LinuxARM)	1m 2s
linux (ubuntu:trusty)	1s
linux (ubuntu:xenial)	1s
debian-unstale (s390x/debian:unstable-slim, s390x, Linux)	59s
linux (ubuntu:bionic)	1s
linux (ubuntu:focal)	1s
debian-unstale (riscv64/debian:unstable-slim, riscv64, Linux)	1m 4s
linux (debian:stretch)	37s
linux (ubuntu:trusty, indigo)	1s
linux (ubuntu:xenial, kinetic)	1s
linux (ubuntu:bionic, meodic)	1s
linux (ubuntu:focal, noetic)	1s
linux (osrf/ubuntu_armhf:trusty)	1s
linux (osrf/ubuntu_armhf:xenial)	1s
linux (osrf/ubuntu_arm64:xenial)	1s
linux (aarch64, arm64v8/ubuntu:bionic)	39s
linux (aarch64, arm64v8/ubuntu:focal)	39s
linux (osrf/debian_arm64:stretch)	37s
linux (amd64/debian:unstable)	39s
linux (amd64, amd64/debian:unstable)	40s
linux (aarch64, arm64v8/debian:buster)	39s
linux (arm, arm32v5/debian:jessie)	39s
linux (arm, arm32v7/debian:jessie)	39s
linux (i386, i386/debian:unstable)	36s
linux (i386, i386/debian:buster)	37s
linux (mips64el, loongnix/debian:buster)	38s
linux (ppc64le, ppc64le/debian:buster)	1s
	18m 41s

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