[CI] Stop using images for git-based CI jobs

The images containing nighly builds of the current
development branch of the core and staging modules
are no longer up-to-date, because they are no longer
updated automatically. One cannot even update them
manually by triggering a pipeline. The only possibility
is to build them locally and push them to the registry
manually.

This is not a viable workflow to me. Hence we switch
to building all dependencies in this case. Once there
are nighly build images again, we can revert the change
if we think it takes up to much resources.

.gitlab-ci.yml

 ---
 # Install external dependencies
-before_script:
-  - duneci-install-module https://gitlab.dune-project.org/extensions/dune-alugrid.git
-  - duneci-install-module https://gitlab.dune-project.org/extensions/dune-subgrid.git
-  - duneci-install-module https://gitlab.dune-project.org/extensions/dune-vtk.git
-  - duneci-install-module https://gitlab.dune-project.org/fufem/dune-matrix-vector.git
+
+# For release-based jobs, we use corresponding images,
+# that already contain all core and staging dependencies.
+.release_based_job:
+  before_script:
+    - duneci-install-module https://gitlab.dune-project.org/extensions/dune-alugrid.git
+    - duneci-install-module https://gitlab.dune-project.org/extensions/dune-subgrid.git
+    - duneci-install-module https://gitlab.dune-project.org/extensions/dune-vtk.git
+    - duneci-install-module https://gitlab.dune-project.org/fufem/dune-matrix-vector.git
+
+# For branch-based-based jobs, we need to install all dependencies manually.
+.branch_base_job:
+  before_script:
+    - . /duneci/bin/duneci-init-job
+    - duneci-install-module https://gitlab.dune-project.org/core/dune-common.git
+    - duneci-install-module https://gitlab.dune-project.org/core/dune-geometry.git
+    - duneci-install-module https://gitlab.dune-project.org/core/dune-localfunctions.git
+    - duneci-install-module https://gitlab.dune-project.org/staging/dune-uggrid.git
+    - duneci-install-module https://gitlab.dune-project.org/core/dune-grid.git
+    - duneci-install-module https://gitlab.dune-project.org/core/dune-istl.git
+    - duneci-install-module https://gitlab.dune-project.org/staging/dune-typetree.git
+    - duneci-install-module https://gitlab.dune-project.org/staging/dune-functions.git
+    - duneci-install-module https://gitlab.dune-project.org/extensions/dune-alugrid.git
+    - duneci-install-module https://gitlab.dune-project.org/extensions/dune-subgrid.git
+    - duneci-install-module https://gitlab.dune-project.org/extensions/dune-vtk.git
+    - duneci-install-module https://gitlab.dune-project.org/fufem/dune-matrix-vector.git
+
+
 
 # The 2.9 release is the one in Debian 12 ('bookworm', 'stable' at the time of writing)
 dune:2.9 debian-11 gcc-10 C++20:
+  extends: .release_based_job
   variables:
     DUNECI_BRANCH: releases/2.9
   image: registry.dune-project.org/docker/ci/dune:2.9-debian-11-gcc-10-20
-  before_script:
   script: duneci-standard-test
 
 # The 2.10 release is the one in Debian 13 ('trixie', 'testing' at the time of writing)
 # To test against 2.10 we need an image with the corresponding version of the core modules.
 # Unfortunately, there is no 2.10 image with a recent enough compiler.
 dune:2.10 debian-11 gcc-10  C++20:
+  extends: .release_based_job
   variables:
     DUNECI_BRANCH: releases/2.10
   image: registry.dune-project.org/docker/ci/dune:2.10-debian-11-gcc-10-20
@@ -25,11 +49,19 @@ dune:2.10 debian-11 gcc-10  C++20:
 
 # Also test with the current development branch
 dune:git debian-11 clang-13  C++20:
-  image: registry.dune-project.org/docker/ci/dune:git-debian-11-clang-13-20
+  extends: .branch_base_job
+#  image: registry.dune-project.org/docker/ci/dune:git-debian-11-clang-13-20
+  image: registry.dune-project.org/docker/ci/debian:11
+  variables:
+    DUNECI_TOOLCHAIN: clang-13-20
   script: duneci-standard-test
 
 dune:git debian-11 gcc-10  C++20:
-  image: registry.dune-project.org/docker/ci/dune:git-debian-11-gcc-10-20
+  extends: .branch_base_job
+#  image: registry.dune-project.org/docker/ci/dune:git-debian-11-gcc-10-20
+  image: registry.dune-project.org/docker/ci/debian:11
+  variables:
+    DUNECI_TOOLCHAIN: gcc-10-20
   script: duneci-standard-test
 
 # Check for spelling mistakes in text