base: Export constructor of Control.Exception.Backtrace.Backtraces

The original CLC proposal indeed proposed that these should be exposed, yet the implementation did not reflect this 1.

Addresses #25753.

libraries/base/src/Control/Exception/Backtrace.hs

@@ -51,7 +51,7 @@ module Control.Exception.Backtrace
     , getBacktraceMechanismState
     , setBacktraceMechanismState
       -- * Collecting backtraces
-    , Backtraces
+    , Backtraces(..)
     , displayBacktraces
     , collectBacktraces
     ) where