release: Finish preparation for 4.2.0

.release.cfg

@@ -5,10 +5,13 b' done = false'
 done = true
 
 [task:fixes_on_stable]
+done = true
 
 [task:pip2nix_generated]
+done = true
 
 [task:changelog_updated]
+done = true
 
 [task:generate_api_docs]
 done = true
@@ -17,7 +20,7 b' done = true'
 done = true
 
 [release]
-state = in_progress
+state = prepared
 version = 4.2.0
 
 [task:rc_tools_pinned]