Update CHANGELOG

[ci skip]

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
+v 8.0.6
+  - Fix loading spinner sometimes not being hidden on Merge Request tab switches
+
 v 8.0.5
   - Correct lookup-by-email for LDAP logins
-  - Fix loading spinner sometimes not being hidden on Merge Request tab switches
 v 8.0.4
   - Fix Message-ID header to be RFC 2111-compliant to prevent e-mails being dropped (Stan Hu)