Add v5.8.0 to CHANGELOG

(cherry picked from commit 4a55a17)

Author: kategengler

CHANGELOG.md

@@ -1,13 +1,9 @@
 # Ember Changelog
 
-## v5.8.0-beta.2 (April 1, 2024)
+## v5.8.0 (April 15, 2024)
 
 - [#20672](https://github.com/emberjs/ember.js/pull/20672) [BUGFIX] Restore `{{this.attrs.foo}}` deprecation from the 3.x era. The API was accidentally not removed in 4.0 but the deprecation was removed.
 
-## v5.8.0-beta.1 (March 4, 2024)
-
-- No user-facing changes that were not backported.
-
 ## v5.7.0 (March 4, 2024)
 
 - [#20639](https://github.com/emberjs/ember.js/pull/20639) [FEATURE] Add an optional feature "no-implicit-route-model" to allow the removal of the implicit loading of a model per [RFC #774](https://rfcs.emberjs.com/id/0774-implicit-record-route-loading).