Fix for lua 5.5 compatibility, for-loop variables are read only

[hcartiaux]

In lua 5.5, for-loop variables are now read-only, this change produces a bunch of errors similar to this one.

/usr/bin/lua: error loading module 'utils' from file './src/utils.lua':
        ./src/utils.lua:421: attempt to assign to const variable 'v'
stack traceback:
        [C]: in ?
        [C]: in global 'require'
        ./src/colorize.lua:43: in main chunk
        [C]: in global 'require'
        ./src/lmod.in.lua:110: in main chunk
        [C]: in ?

This PR attempts to fix this with minimal changes while trying to maintain code styling.

[LecrisUT]

Should have checked PRs 🙃. I've made #811, but the tests are failing there. Want to cross review each other?

[hcartiaux]

Should have checked PRs 🙃. I've made #811, but the tests are failing there. Want to cross review each other?

Wow, I also missed #807 actually. You made me realize I've missed quite a few occurrences.

I prefer my approach using a different variable name inside the loop, it's less confusing to me.

Once we agree on the styling, we can import the changes of one PR into the other, fix the tests and close the remaining PR