AST-1553 Remove IDG from Ubuntu 20 build; Add Ubuntu 24 build

• Since IDG no longer supports Ubuntu 20 (it uses CMake 3.17, while Ubuntu 20 has CMake 3.16), remove it from the Ubuntu 20 CI build.
• Add a basic Ubuntu 24 build on CI.

.gitlab-ci.common.yml

@@ -37,8 +37,8 @@ versioning:
   script:
     # Unshallowing ensures that 'git log' works
     - git fetch --unshallow
-    - echo BASE_IMAGE_2204=${CI_REGISTRY_IMAGE}/base_ubuntu20:$(git log -n 1 --pretty=format:%H -- docker/ubuntu_22_04_base) > versions.env
-    - echo BASE_IMAGE_2404=${CI_REGISTRY_IMAGE}/base_ubuntu22:$(git log -n 1 --pretty=format:%H -- docker/ubuntu_24_04_base) >> versions.env
+    - echo BASE_IMAGE_2204=${CI_REGISTRY_IMAGE}/base_ubuntu22:$(git log -n 1 --pretty=format:%H -- docker/ubuntu_22_04_base) > versions.env
+    - echo BASE_IMAGE_2404=${CI_REGISTRY_IMAGE}/base_ubuntu24:$(git log -n 1 --pretty=format:%H -- docker/ubuntu_24_04_base) >> versions.env
     - cat versions.env
   artifacts:
     reports: