Bumps changelog version to 2.7.0

Updates the CHANGELOG.md file to add a changelog entry for a new 2.7.0 version.

Author: laminas-bot

CHANGELOG.md

@@ -2,6 +2,28 @@
 
 All notable changes to this project will be documented in this file, in reverse chronological order by release.
 
+## 2.7.0 - TBD
+
+### Added
+
+- Nothing.
+
+### Changed
+
+- Nothing.
+
+### Deprecated
+
+- Nothing.
+
+### Removed
+
+- Nothing.
+
+### Fixed
+
+- Nothing.
+
 ## 2.6.0 - 2023-12-14