Rails Edge requires Ruby >= 3.1

[ericproulx]

We need to fix the edge workflow for rails_edge since it's ruby >= 3.1.0

Because every version of rails depends on Ruby >= 3.1.0
and rails_edge.gemfile depends on rails >= 0,
Ruby >= 3.1.0 is required.
So, because current Ruby version is = 2.7.8,
version solving has failed.
Error: The process '/opt/hostedtoolcache/Ruby/2.7.8/x64/bin/bundle' failed with exit code 6