Allow to publish packages with test dependencies not in the registry

CHANGELOG.md

@@ -23,6 +23,8 @@ Other improvements:
   overwrite the file if the marker isn't present, assuming that the file was
   manually created or edited, not generated by Spago itself.
 - migrated tests to the `spec-node` runner.
+- `spago publish` now allows to publish a package with some test (but only
+  test!) dependencies not present in the registry.
 
 ## [0.21.0] - 2023-05-04