build: apply the fix suggested by kit-ty-kate

here https://github.com/ocaml/opam-repository/pull/19031
3 jobs for master in 5 minutes and 38 seconds (queued for 3 seconds)
Status Name Job ID Coverage
  Build
passed build #244079

00:01:53

 
  Test
passed test_opam_test #244080

00:02:55

 
  Release
passed release #244081

00:00:49