Prepare 0.8.0 release (#704)

Author: akihironitta

CHANGELOG.md

@@ -5,7 +5,7 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [Unreleased]
+## [0.8.0] - 2026-07-21
 
 ### Added
 
@@ -22,7 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Removed
 
-- Dropped support for PyTorch 2.9
+- Dropped support for PyTorch 2.9 ([#681](https://github.com/pyg-team/pyg-lib/pull/681))
 
 ### Fixed