replaced string arguments by reference

4 jobs for issue/interface_cleanup_strings in 19 minutes and 5 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #6772
debian:10 clang-6-libcpp-17

00:19:05

passed #6771
debian:10 gcc-8-17

00:12:39

passed #6773
debian:9 gcc-6-14

00:10:48

passed #6774
ubuntu:18.04 clang-6-17

00:17:22