Merge branch 'ci-fedora-31' into 'master'

CI: Bump Fedora from 30 to 31

See merge request sane-project/backends!230

.gitlab-ci.yml

@@ -77,8 +77,8 @@ debian-10-full:
     - doc/sanei-html
     expire_in: 1 day
 
-fedora-30-clang:
-  image: $REGISTRY_HUB:fedora-30-clang
+fedora-31-clang:
+  image: $REGISTRY_HUB:fedora-31-clang
   variables:
     CONFIGURE_OPTS: "$CONFIGURE_MINI $CONFIGURE_FULL"
   <<: *compile_definition