Update puppetlabs_spec_helper requirement from ~> 7.0 to ~> 8.0

Updates the requirements on [puppetlabs_spec_helper](https://github.com/puppetlabs/puppetlabs_spec_helper) to permit the latest version.
- [Release notes](https://github.com/puppetlabs/puppetlabs_spec_helper/releases)
- [Changelog](https://github.com/puppetlabs/puppetlabs_spec_helper/blob/main/CHANGELOG.md)
- [Commits](puppetlabs/puppetlabs_spec_helper@v7.0.0...v8.0.0)

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

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

Gemfile

@@ -37,7 +37,7 @@ group :development do
 end
 group :development, :release_prep do
   gem "puppet-strings", '~> 4.0',         require: false
-  gem "puppetlabs_spec_helper", '~> 7.0', require: false
+  gem "puppetlabs_spec_helper", '~> 8.0', require: false
 end
 group :system_tests do
   gem "puppet_litmus", '~> 1.0',   require: false, platforms: [:ruby, :x64_mingw]