Mark dedup complex test as flaky

- Sometimes fails with HTTP code 525, SSL handshake failure

cabal-testsuite/PackageTests/ProjectImport/DedupUsingConfigFromComplex/cabal.test.hs

 import Test.Cabal.Prelude
 import Data.Function ((&))
 
-main = cabalTest . recordMode RecordMarked $ do
+main = cabalTest . flakyIfCI 10927. recordMode RecordMarked $ do
   let log = recordHeader . pure
 
   log "check \"using config from message\" with URI imports"