chore(users/Profpatsch/*): more cabal maintenance

Change-Id: Ib1714abce2815873eb50dbeac088e812fa9098ab
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8686
Tested-by: BuildkiteCI
Reviewed-by: Profpatsch <mail@profpatsch.de>
Autosubmit: Profpatsch <mail@profpatsch.de>

users/Profpatsch/mailbox-org/mailbox-org.cabal

@@ -1,4 +1,4 @@
-cabal-version:      2.4
+cabal-version:      3.0
 name:               mailbox-org
 version:            0.1.0.0
 author:             Profpatsch
@@ -10,7 +10,9 @@ executable mailbox-org
     build-depends:
         base >=4.15 && <5,
         my-prelude,
+        pa-prelude,
         pa-label,
+        pa-error-tree,
         exec-helpers,
         netencode,
         text,