Repor: oxcaml fails with unlicked dune pkg

If we instead do a `dune pkg lock` first, it will proceed to build

Author: shonfeder

test/blackbox-tests/test-cases/pkg/oxcaml/run.t

@@ -0,0 +1,13 @@
+  $ dune init proj oxcaml-test .
+  $ sed -i -e 's/depends ocaml/depends (ocaml-variants (= 5.2.0+ox))/' dune-project
+  $ cat > dune-workspace <<EOF
+  > (lang dune 3.21)
+  >
+  > (pkg enabled)
+  >
+  > (repository
+  >   (name oxcaml)
+  >   (url git+https://github.com/oxcaml/opam-repository))
+  >
+  > (lock_dir (repositories overlay oxcaml upstream))
+  $ dune build