update CI configuration to not test C++14 anymore

.gitlab-ci.yml

@@ -10,7 +10,7 @@ variables:
   DUNECI_TEST_LABELS: quick
   DUNE_TEST_EXPECTED_VC_IMPLEMENTATION: SSE2
 
-debian:10 gcc-7-14--expensive:
+debian:10 gcc-7-17--expensive:
   # This image has Vc
   image: registry.dune-project.org/docker/ci/debian:10
   script: duneci-standard-test
@@ -18,7 +18,7 @@ debian:10 gcc-7-14--expensive:
   variables:
     DUNECI_CXXFLAGS: -mavx
     DUNECI_TEST_LABELS: ""
-    DUNECI_TOOLCHAIN: gcc-7-14
+    DUNECI_TOOLCHAIN: gcc-7-17
     DUNE_TEST_EXPECTED_VC_IMPLEMENTATION: AVX
   # require AVX to properly test Vc
   tags: [duneci, "iset:avx"]