ci: Move Coverity from CentOS 8 to CentOS Stream 8

CentOS 8 reach end of life and its YUM repositories were shut down:

STEP 3: RUN yum -y install epel-release     && yum -y install dnf-plugins-core     && yum config-manager --enable powertools     && yum -y --setopt=tsflags='' install         clang 	createrepo_c 	elinks 	file-devel 	gcc 	gcc-c++ 	git-core 	glib2-devel 	glib2-doc 	gobject-introspection-devel 	gtk-doc 	jq 	libyaml-devel 	meson 	ninja-build 	pkgconfig 	python2-devel 	python2-six 	python3-gobject-base 	python36-devel 	python3-rpm-macros 	redhat-rpm-config 	rpm-build 	rpm-devel 	rpmdevtools 	sudo     && yum -y clean all
CentOS Linux 8 - AppStream                      1.1 kB/s |  38  B     00:00
Error: Failed to download metadata for repo 'appstream': Cannot prepare internal mirrorlist: No URLs in mirrorlist

CentOS/sig-cloud-instance-images#190

Author: ppisar

.ci/ci-coverity.sh

@@ -9,8 +9,8 @@ set -e
 set -x
 
 os=centos
-release=8
-repository=docker.io
+release=stream8
+repository=quay.io/centos
 
 # Override the standard tests with the Coverity scan
 mmd_run_docker_tests \