Update CHANGELOG

CHANGELOG.md

 # Changelog
 
-## 0.5.0a1 (`towards_frictionless_4` branch)
-
+## next
+
+## 0.5.0a2 (`towards_frictionless_4` branch)
+- update requirements (validata-core 0.7.0a2)
+- add explicit error message when a tabular data as url can't be retrieved (404)
+- improve error message ([issue](https://git.opendatafrance.net/validata/validata-ui/-/issues/82)]
+ 
+ ## 0.5.0a1 (`towards_frictionless_4` branch)
+ 
 - update requirements
 - adapt to changes in validation report