build: cabal: add missing default-language

Status Job ID Name Coverage
  Stack
failed #10679
stack

 
  Cabal
skipped #10680
cabal
 
  Bench
skipped #10681
bench
 
  Test
skipped #10682
test
 
Name Stage Failure
failed
stack Stack There has been a timeout failure or the job got stuck. Check your timeout limits or try again
No job trace