Update irb requirement from ~> 1.14.3 to ~> 1.15.1

Updates the requirements on [irb](https://github.com/ruby/irb) to permit the latest version.
- [Release notes](https://github.com/ruby/irb/releases)
- [Commits](ruby/irb@v1.14.3...v1.15.1)

---
updated-dependencies:
- dependency-name: irb
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile

@@ -6,7 +6,7 @@ gemspec
 
 group(:development, :test) do
   gem('rake', '~> 13.2.1')
-  gem('irb', '~> 1.14.3')
+  gem('irb', '~> 1.15.1')
   gem('irb-power_assert', '0.4.0')
   gem('perfect_toml', '~> 0.9.0', require: false)
 end