Fix GetGraphForModuleKeys requiring unique Registries

`GetGraphForModuleKeys` was attempting to determine a primary and
secondary registry, but it was doing so by requiring that the Registry
is unique across all deps. Instead, it should simply extract the unique
registries.

private/bufpkg/bufmodule/bufmoduleapi/registry.go

@@ -48,7 +48,7 @@ func getPrimarySecondaryRegistry[T hasModuleFullName](s []T) (string, string, er
  if len(s) == 0 {
  return "", "", syserror.New("must have at least one value in getPrimarySecondaryRegistry")
  }
- registryMap, err := slicesext.ToUniqueValuesMapError(
+ registryMap, err := slicesext.ToValuesMapError(
  s,
  func(e T) (string, error) {
  moduleFullName := e.ModuleFullName()