Removed incorrect depext flag

Author: craff

.github/workflows/main.yml

@@ -33,7 +33,6 @@ jobs:
         uses: avsm/setup-ocaml@v3
         with:
           ocaml-compiler: ${{ matrix.ocaml-compiler }}
-          opam-depext-flags: --with-test
 
       - run: opam install . --deps-only --with-test