fix compiler warning in OTP 20 by removing export_all

[allenan]

I received the following error message when trying to build this project:

===> Compiling _build/default/lib/cli/src/cli_tests.erl failed
_build/default/lib/cli/src/cli_tests.erl:3: export_all flag enabled - all functions will be exported

This PR removes export_all from the cli tests file, which now raises a compiler error in OTP 20. Instead, only run/0 and run/1 are exported.