use relative path in gitsubmodules

.gitmodules

 [submodule "libcdi"]
 	path = libcdi
-	url = git@gitlab.dkrz.de:mpim-sw/libcdi.git
+	url = ../libcdi.git
 [submodule "test/bandit_tests/bandit"]
 	path = test/bandit_tests/bandit
 	url = https://github.com/banditcpp/bandit.git