ci: Drop validate 8.4.4 job.

We no longer support 8.4.4 as it is older than three years.
cabal-install can
still be used with 8.4.4, but just not built with it, and this is tested
by the old-ghcs jobs.

.github/workflows/validate.yml

@@ -67,7 +67,7 @@ jobs:
     strategy:
       matrix:
         os: ["ubuntu-latest", "macos-latest", "windows-latest"]
-        ghc: ["9.8.1", "9.6.3", "9.4.8", "9.2.8", "9.0.2", "8.10.7", "8.8.4", "8.6.5", "8.4.4"]
+        ghc: ["9.8.1", "9.6.3", "9.4.8", "9.2.8", "9.0.2", "8.10.7", "8.8.4", "8.6.5"]
         exclude:
           # corrupts GHA cache or the fabric of reality itself, see https://github.com/haskell/cabal/issues/8356
           - os: "windows-latest"