CI: add GHC 9.14 to test matrix (#11910)

GHC 9.14 ships base 4.22 and containers 0.8, newer than the bounds of
serialise, cborg, and haddock-library allow.  Relax them under
impl(ghc >= 9.14) so other lanes are unaffected, and force -fhttp on
the 9.14 lane: given the choice, the solver prefers disabling the
http flag to violating bounds.

.github/workflows/ci.yml

@@ -64,6 +64,11 @@ jobs:
           - ghc: '9.12'
             cabal: 'latest'
             cabalopts: '--ghc-option=-Werror -f-embed_data_files'
+          - ghc: '9.14'
+            cabal: 'latest'
+            # -fhttp: on base 4.22 the solver otherwise prefers
+            # disabling the http flag to using allow-newer
+            cabalopts: '--ghc-option=-Werror -fhttp'
 
     steps:
     - uses: actions/checkout@v7