Codename check: use Case instead of Ifs

[teward]

Case conditionals are more expandable for multiple string matches and in the long term for future version support will greatly reduce the codename checks - it's easier to simply add a codename to the case list than to add multiple if checks in a way that ShellCheck will accept. This allows easy adding of any future codename to the supported list without needing to duplicate the if checks for future version matches in a way that Shellcheck would complain about.

[teward]

Dependent on #69 in order to get the shellcheck bits to fix themselves.