Support Rails 7.0 and Ruby 3.1

[moskvin]

• Added Rails 7 as target
• Added Ruby 3.1 as target
• Updated some dev dependencies

[moskvin]

➜ rake spec
Booting PT test dummy app: Using gemfile: ./paper_trail_scrapbook/Gemfile
WARN: Unresolved or ambiguous specs during Gem::Specification.reset:
      diff-lcs (>= 1.2.0, < 2.0)
      Available/installed versions of this gem:
      - 1.5.0
      - 1.4.4
WARN: Clearing out unresolved specs. Try 'gem cleanup <gem>'
Please report a bug if this causes problems.
DEPRECATION WARNING: Using legacy connection handling is deprecated. Please set
`legacy_connection_handling` to `false` in your application.

The new connection handling does not support `connection_handlers`
getter and setter.

Read more about how to migrate at: https://guides.rubyonrails.org/active_record_multiple_databases.html#migrate-to-the-new-connection-handling
 (called from require at ./.rbenv/versions/3.1.1/lib/ruby/gems/3.1.0/gems/zeitwerk-2.5.4/lib/zeitwerk/kernel.rb:35)
Run options: include {:focus=>true}

All examples were filtered out; ignoring {:focus=>true}

Randomized with seed 17922
..................................................

Finished in 0.53918 seconds (files took 1.91 seconds to load)
50 examples, 0 failures

Randomized with seed 17922

Coverage report generated for RSpec to ./paper_trail_scrapbook/coverage. 231 / 235 LOC (98.3%) covered.