[CI] Test with 2.10, update a few jobs

2.9 and 2.10 are what is currently in Debian stable and testing,
respectively.

.gitlab-ci.yml

 ---
 # Install external dependencies
 before_script:
-  - duneci-install-module https://git.imp.fu-berlin.de/agnumpde/dune-matrix-vector.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:
   variables:
     DUNECI_BRANCH: releases/2.9
@@ -10,8 +11,22 @@ dune:2.9 debian-11 gcc-10 C++20:
   before_script:
   script: duneci-standard-test
 
-dune:git ubuntu-20-04 clang-10  C++17:
-  image: registry.dune-project.org/docker/ci/dune:git-ubuntu-20.04-clang-10-17
+# The 2.10 release is the one in Debian 13 ('trixie', 'testing' at the time of writing)
+dune:2.10 debian-11 clang-13  C++20:
+  variables:
+    DUNECI_BRANCH: releases/2.10
+  image: registry.dune-project.org/docker/ci/dune:git-debian-11-clang-13-20
+  script: duneci-standard-test
+
+dune:2.10 debian-11 gcc-10  C++20:
+  variables:
+    DUNECI_BRANCH: releases/2.10
+  image: registry.dune-project.org/docker/ci/dune:git-debian-11-gcc-10-20
+  script: duneci-standard-test
+
+# 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
   script: duneci-standard-test
 
 dune:git debian-11 gcc-10  C++20: