[ci] change ubuntu version in gitlab-ci to 22.04

What this MR does / why does DuMux need it:

3.7 needs to be tested on ubuntu 22.04 before removing the 20.04 image from dumux-docker-ci

Required for dumux-docker-ci#11 (closed)

Before you request a review from someone, make sure to revise the following points:

• does the new code follow the style guide?
• do the test pipelines pass? (see guide on how to run pipelines for a merge request)
• is the code you changed and/or the new code you wrote covered in the test suite? (if not, extend the existing tests or write new ones)
• does your change affect public interfaces or behavior, or, does it introduce a new feature? If so, document the change in CHANGELOG.md.
• is the list of the header includes complete? ("include what you use")
• all files have to end with a \n character. Make sure there is no \ No newline at end of file comment in "Changes" of this MR.

.gitlab-ci.yml

@@ -23,7 +23,7 @@ workflow:
 # pipeline on a related merge request already. If yes, we simply return
 # to propagate that pipeline status on master. Otherwise, we trigger a new run.
 check-pipeline-status:
-  image: $IMAGE_REGISTRY_URL/full:dune-$DUMUX_CI_DUNE_LATEST_RELEASE-gcc-ubuntu-20.04
+  image: $IMAGE_REGISTRY_URL/full:dune-$DUMUX_CI_DUNE_LATEST_RELEASE-gcc-ubuntu-22.04
   stage: check-status
   rules:
     - if: $CI_PIPELINE_SOURCE == "schedule"
@@ -108,17 +108,17 @@ full-dune-latest-release-gcc-cpp-20:
 full-dune-latest-release-gcc:
   extends: .base-trigger
   variables:
-    IMAGE: $IMAGE_REGISTRY_URL/full:dune-$DUMUX_CI_DUNE_LATEST_RELEASE-gcc-ubuntu-20.04
+    IMAGE: $IMAGE_REGISTRY_URL/full:dune-$DUMUX_CI_DUNE_LATEST_RELEASE-gcc-ubuntu-22.04
 
 minimal-dune-latest-release-gcc:
   extends: .base-trigger
   variables:
-    IMAGE: $IMAGE_REGISTRY_URL/minimal:dune-$DUMUX_CI_DUNE_LATEST_RELEASE-gcc-ubuntu-20.04
+    IMAGE: $IMAGE_REGISTRY_URL/minimal:dune-$DUMUX_CI_DUNE_LATEST_RELEASE-gcc-ubuntu-22.04
 
 full-dune-latest-release-clang:
   extends: .base-trigger
   variables:
-    IMAGE: $IMAGE_REGISTRY_URL/full:dune-$DUMUX_CI_DUNE_LATEST_RELEASE-clang-ubuntu-20.04
+    IMAGE: $IMAGE_REGISTRY_URL/full:dune-$DUMUX_CI_DUNE_LATEST_RELEASE-clang-ubuntu-22.04
 
 ################################################
 # trigger test pipelines of downstream modules #