Ensure we are not using backticks to get shell command outputs
As per https://docs.gitlab.com/ee/development/shell_commands.html#do-not-use-the-backticks, the use of backticks to run shell commands and get their output is discouraged. We have a few instances where we still use it.
With !2761 (merged) we did a similar cleanup. We should do another one to get backtick issue fixed too.