[PATCH 2/4] docs/devel: update references to centos to later version

[Alex Bennée]

>From the website:

"After May 31, 2024, CentOS Stream 8 will be archived and no further
updates will be provided."

We have updated a few bits but there are still references that need
fixing.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
---
 docs/devel/testing.rst | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/docs/devel/testing.rst b/docs/devel/testing.rst
index fa28e3ecb2..c312465fa7 100644
--- a/docs/devel/testing.rst
+++ b/docs/devel/testing.rst
@@ -387,9 +387,9 @@ make target):
 
 .. code::
 
-  make docker-test-build@centos8
+  make docker-test-build@centos9
 
-This will create a container instance using the ``centos8`` image (the image
+This will create a container instance using the ``centos9`` image (the image
 is downloaded and initialized automatically), in which the ``test-build`` job
 is executed.
 
@@ -410,8 +410,8 @@ locally by using the ``NOCACHE`` build option:
 Images
 ~~~~~~
 
-Along with many other images, the ``centos8`` image is defined in a Dockerfile
-in ``tests/docker/dockerfiles/``, called ``centos8.docker``. ``make 
docker-help``
+Along with many other images, the ``centos9`` image is defined in a Dockerfile
+in ``tests/docker/dockerfiles/``, called ``centos9.docker``. ``make 
docker-help``
 command will list all the available images.
 
 A ``.pre`` script can be added beside the ``.docker`` file, which will be
-- 
2.39.2