Add role for `rbenv`

[jansroka]

We install rbenv via brew, but there is not set up for this.

On Sonoma I ran into this issue: rbenv/rbenv#766 ...I could only install ruby if I ran it like this:

LDFLAGS= rbenv install 3.2.2

Otherwise I'd get this error:

14:12:45 ~ $ rbenv install 3.2.2 --verbose
Downloading ruby-3.2.2.tar.gz...
-> https://cache.ruby-lang.org/pub/ruby/3.2/ruby-3.2.2.tar.gz
/var/folders/m4/x0s22spn2xg87tjpm1n81dfm0000gn/T/ruby-build.20231009141249.11065.uthb6q ~
Installing ruby-3.2.2...
mkdir: cannot create directory ‘/usr/local/opt’: Permission denied