copilot-theorem: Bump what4 upper bound to < 1.7. Refs #514.

what4 has seen a new release 1.6, but copilot-theorem needs versions
strictly lower than 1.6. This version is API-compatible for all features
used by copilot-theorem, but it includes support for GHC 9.8, which we
want to also support.

Author: fdedden

copilot-theorem/copilot-theorem.cabal

@@ -61,7 +61,7 @@ library
                           , random                >= 1.1 && < 1.3
                           , transformers          >= 0.5 && < 0.7
                           , xml                   >= 1.3 && < 1.4
-                          , what4                 >= 1.3 && < 1.6
+                          , what4                 >= 1.3 && < 1.7
 
                           , copilot-core          >= 3.19.1 && < 3.20
                           , copilot-prettyprinter >= 3.19.1 && < 3.20