[Enhancement]: Letterboxd social icon is not up to date

[pedrohff]

What you'd like to propose?

This pull request #799 brought the Letterboxd icon to the theme, but it uses and outdated version of it.
This is the website's logo:

This is the logo being used by the theme currently:

I would like to make this one the default one:

Does it make sense?
Here are some other options we could use: https://icon-sets.iconify.design/?query=letterboxd

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