Support ghc-9.8.1

[Erik de Castro Lopo]

Currently builds with ghc-9.8.1 with this patch:

diff --git a/async.cabal b/async.cabal
index 6814a84..8355526 100644
--- a/async.cabal
+++ b/async.cabal
@@ -66,7 +66,7 @@ library
     if impl(ghc>=7.1)
         other-extensions: Trustworthy
     exposed-modules:     Control.Concurrent.Async
-    build-depends:       base     >= 4.3     && < 4.19,
+    build-depends:       base     >= 4.3     && < 4.20,
                          hashable >= 1.1.2.0 && < 1.5,
                          stm      >= 2.2     && < 2.6
 

So a Hackage metadata edit would be sufficient.

Let me know if you would prefer a PR.

[Erik de Castro Lopo]

Thanks!