Fix ruby DSL requirement matching for head and prerelease rubies

[deivid-rodriguez]

What was the end-user or developer problem that led to this PR?

While working on #5715, my changes made this bug surface.

With the following Gemfile

source "https://rubygems.org"

ruby ">= 3.2.0"

And

$ ruby -v
ruby 3.2.0preview1 (2022-04-03 master f801386f0c) [arm64-darwin21]

Currently Bundler is happy

$ bundle
The Gemfile specifies no dependencies
Resolving dependencies...
Bundle complete! 0 Gemfile dependencies, 1 gem now installed.
Use `bundle info [gemname]` to see where a bundled gem is installed.

What is your fix for the problem, implemented in this PR?

My fix is to pass the resolver an actual string for the current Ruby version that considers prereleases.

After this fix, the previous case gives the expected error:

$ bundle
Your Ruby version is 3.2.0.preview1, but your Gemfile specified >= 3.2.0

Make sure the following tasks are checked

• Describe the problem / feature
• Write tests for features and bug fixes
• Write code to solve the problem
• Make sure you follow the current code style and write meaningful commit messages without tags

[deivid-rodriguez]

Merging since it unblocks the fix for #5715.