Fix CI: use the same Ruby version in CI and Gemfile.lock

[handshake-enthusiast]

No description provided.

[handshake-enthusiast]

While this worked it would be better to use the same Ruby version (3.0.3) which is used in Gemfile.lock. I'm changing to that version.

[handshake-enthusiast]

Before:

Run ruby/setup-ruby@v1
  with:
    ruby-version: 3
    bundler-cache: true
    
Downloading Ruby
  https://github.com/ruby/ruby-builder/releases/download/toolcache/ruby-3.2.0-ubuntu-22.04.tar.gz

Ruby 3.2.0 couldn't install nokogiri during Run ./bin/build.

After:

Run ruby/setup-ruby@v1
  with:
    ruby-version: 3.0.3
    bundler-cache: true
    
Downloading Ruby
  https://github.com/ruby/ruby-builder/releases/download/toolcache/ruby-3.0.3-ubuntu-22.04.tar.gz

Very strange previously it was installing Ruby 3.2 instead of 3.0 even though https://github.com/ruby/setup-ruby#supported-version-syntax says:

short version like '2.6', automatically using the latest release matching that version (2.6.10)

[handshake-enthusiast]

Explained ruby/setup-ruby#442 (comment)

[handshake-enthusiast]

You can merge this PR in order to make other PRs green (e.g. #170 and #171).

@pinheadmz @nodech (not sure who else is active and has merge rights)