ci: switch GCC build in GitLab pipeline to GCC 15 (from GCC 14)

Author: striezel

.gitlab-ci.yml

@@ -1,7 +1,7 @@
 # Use the official gcc image, based on debian.
 # It can use version tags as well, like gcc:8.5.
 # See https://hub.docker.com/_/gcc/ for more info.
-image: gcc:14
+image: gcc:15
 
 variables:
   GIT_SUBMODULE_STRATEGY: recursive
@@ -10,7 +10,7 @@ build_gcc:
   stage: build
   before_script:
     - apt-get update
-    - apt-get -y install catch cmake g++ libboost-dev libxml2 libxml2-dev zlib1g-dev
+    - apt-get -y install catch2 cmake g++ libboost-dev libxml2 libxml2-dev zlib1g-dev
     - apt-get install -y firefox-esr --no-install-recommends
     # Remove parts of the submodule that are not used but would get into CI's
     # way when linting.