ci benchmark: ensure installing old versions

Benchmark CI is failing because csv 3.3.0 isn't installed: https://github.com/ruby/csv/actions/runs/15481241182/job/43587350229#step:5:10 ```text /opt/hostedtoolcache/Ruby/3.4.4/x64/lib/ruby/3.4.0/rubygems/dependency.rb:303:in 'Gem::Dependency#to_specs': Could not find 'csv' (= 3.3.0) - did find: [csv-3.3.2,csv-3.0.2,csv-3.0.1] (Gem::MissingSpecVersionError) ```