[CI] Work around CA issues in gitlab-runner for submodules.

See https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/2148.

.gitlab-ci.yml

 ---
 variables:
-  GIT_SUBMODULE_STRATEGY: recursive
+# work around https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/2148
+# value should be "recursive" without workaround
+  GIT_SUBMODULE_STRATEGY: none
 
 before_script:
+# work around https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/2148
+- git submodule sync --recursive
+- git submodule update --init --recursive
+# end workaround
 - ( cd python/loopy && git am ../../patches/loopy/0001-Allow-using-globalargs-as-base-storage.patch )
 - ( cd python/loopy && git am ../../patches/loopy/Current.patch )
 - ( cd dune/perftool/vectorclass && git am ../../patches/vectorclass/0001-Better-implementation-of-horizontal_add.patch )