ci: fix git submodule update --init race condition

CMakeLists.txt

@@ -10,10 +10,24 @@ set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
 OPTION(TIDY "Run clang-tidy" OFF)
 OPTION(VALGRIND "Run valgrind" OFF)
 OPTION(SAN "Build with sanitize flags" OFF)
+if(DEFINED ENV{CI})
+  if($ENV{CI} MATCHES "true")
+    message(STATUS "We're in CI!")
+    OPTION(IS_CI "Are we in CI?" ON)
+  endif()
+else()
+  OPTION(IS_CI "Are we in CI?" OFF)
+endif()
 
 find_package(Git QUIET)
 if(GIT_FOUND AND EXISTS "${PROJECT_SOURCE_DIR}/.git")
-  option(GIT_SUBMODULE "Check submodules during build" ON)
+  if(IS_CI)
+    # there seems to be a race condition so the submodules are simply
+    # initialized/updated in a separate step and therefore this is not needed
+    option(GIT_SUBMODULE "Check submodules during build" OFF)
+  else()
+    option(GIT_SUBMODULE "Check submodules during build" ON)
+  endif()
   if(GIT_SUBMODULE)
     message(STATUS "Update submodule(s)")
     message(STATUS "Current source dir: ${CMAKE_CURRENT_SOURCE_DIR}")