Update rubocop-ast requirement from = 1.31.2 to = 1.31.3

Updates the requirements on [rubocop-ast](https://github.com/rubocop/rubocop-ast) to permit the latest version.
- [Release notes](https://github.com/rubocop/rubocop-ast/releases)
- [Changelog](https://github.com/rubocop/rubocop-ast/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop-ast@v1.31.2...v1.31.3)

---
updated-dependencies:
- dependency-name: rubocop-ast
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

rubocop-govuk.gemspec

@@ -16,7 +16,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "rake", "~> 13"
 
   spec.add_dependency "rubocop", "1.63.4"
-  spec.add_dependency "rubocop-ast", "1.31.2"
+  spec.add_dependency "rubocop-ast", "1.31.3"
   spec.add_dependency "rubocop-rails", "2.24.1"
   spec.add_dependency "rubocop-rake", "0.6.0"
   spec.add_dependency "rubocop-rspec", "2.29.1"