gitlab-ci: Use CentOS9 for Coverity builds

The Fedora 34 container is not available anymore. And we need gcc 11
as scan.coverity.com is on version 2022.6 supporting only gcc 11.

See
https://dev.sig-docs.synopsys.com/polaris/topics/r_coverity-compatible-platforms_2022.6.html

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>

.gitlab-ci.yml

@@ -2,7 +2,6 @@
 variables:
   BUILD_IMAGES_PROJECT: libssh/build-images
   CENTOS9_BUILD: buildenv-c9s
-  COVERITY_BUILD: buildenv-coverity
   FEDORA_BUILD: buildenv-fedora
   MINGW_BUILD: buildenv-mingw
   TUMBLEWEED_BUILD: buildenv-tumbleweed
@@ -522,7 +521,7 @@ visualstudio/x86:
 
 coverity:
   stage: analysis
-  image: $CI_REGISTRY/$BUILD_IMAGES_PROJECT:$COVERITY_BUILD
+  image: $CI_REGISTRY/$BUILD_IMAGES_PROJECT:$CENTOS9_BUILD
   script:
     - mkdir obj && cd obj
     - wget https://scan.coverity.com/download/linux64 --post-data "token=$COVERITY_SCAN_TOKEN&project=$COVERITY_SCAN_PROJECT_NAME" -O /tmp/coverity_tool.tgz