Update commonmarker requirement from >= 0.23.7, < 2.6.0 to >= 0.23.7, < 2.7.0

Updates the requirements on [commonmarker](https://github.com/gjtorikian/commonmarker) to permit the latest version.
- [Release notes](https://github.com/gjtorikian/commonmarker/releases)
- [Changelog](https://github.com/gjtorikian/commonmarker/blob/main/CHANGELOG.md)
- [Commits](gjtorikian/commonmarker@v0.23.7...v0.23.12)

---
updated-dependencies:
- dependency-name: commonmarker
  dependency-version: 0.23.12
  dependency-type: direct:production
...

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

Author: dependabot[bot]

jekyll-commonmark-ghpages.gemspec

@@ -16,7 +16,7 @@ Gem::Specification.new do |spec|
 
   spec.add_runtime_dependency "jekyll", ">= 3.9", "< 4.0"
   spec.add_runtime_dependency "jekyll-commonmark", "~> 1.4.0"
-  spec.add_runtime_dependency "commonmarker", ">= 0.23.7", "< 2.6.0"
+  spec.add_runtime_dependency "commonmarker", ">= 0.23.7", "< 2.7.0"
   spec.add_runtime_dependency "rouge", ">= 2.0", "< 5.0"
 
   spec.add_development_dependency "rspec", "~> 3.0"