Log message:
devel/ruby-observer: update Ruby's version in comment

Ruby 3.3.7 still have the same version of observer gem.

Log message:
devel/ruby-observer: restrict Ruby's version

Restrict Ruby's version (not for Ruby 3.4) since Ruby 3.3.6 and 3.4.1 have
this gem of the same version as default gem.

Log message:
devel/ruby-observer: add package version 0.1.2

This pacakge is required by newer graphics/ruby-RMagick package.

Observer

The Observer pattern (also known as publish/subscribe) provides a simple
mechanism for one object to inform a set of interested third-party objects
when its state changes.