Prepare azure_core 0.26.0 for release (Azure#2788)

Author: chlowell

sdk/identity/azure_identity/CHANGELOG.md

@@ -1,8 +1,6 @@
 # Release History
 
-## 0.26.0 (Unreleased)
-
-### Features Added
+## 0.26.0 (2025-07-15)
 
 ### Breaking Changes
 
@@ -11,10 +9,6 @@
 - Replaced `azure_core::process::Executor` with `azure_identity::process::Executor`.
 - Renamed `azure_core::date` module to `azure_core::time`
 
-### Bugs Fixed
-
-### Other Changes
-
 ## 0.25.0 (2025-06-10)
 
 ### Bugs Fixed