ragel.yml - use 'bundle exec rake' instead of 'rake'

[MSP-Greg]

Description

Rake 13.1.0 has been released, and the ragel CI is failing in my fork.

BUNDLE_PATH is set by setup/ruby using bundle config --local path <path>, so the gems installed by it are not accessible unless bundle exec is used. Hence, one should always use bundle exec or require 'bundler/setup'.

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