Fix Import/Export labels error

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/24257

For existing labels that have already been created for merge requests or issues, we should avoid keeping the priorities in the hash as they have also been created already and it will throw an error trying to update the label that already has

• Changelog entry added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

marked the task Changelog entry added as completed

marked the task Added for this feature/bug as completed

marked the task Conform by the merge request performance guides as completed

marked the task Conform by the style guides as completed

marked the task Branch has no merge conflicts with master (if it does - rebase it please) as completed

marked the task Added for this feature/bug as incomplete

marked the task Conform by the merge request performance guides as incomplete

marked the task Conform by the style guides as incomplete

marked the task Branch has no merge conflicts with master (if it does - rebase it please) as incomplete

assigned to @DouweM

added ~978334 label

@jameslopez Can we have a spec for this? Or is updating the JSON file enough?

resolved all discussions

assigned to @jameslopez

@DouweM I think updating the JSON is enough, it's basically replicating the exact problem and project_restorer_spec.rb will fail with exact the same error as the original issue.

marked the task Added for this feature/bug as completed

marked the task Conform by the merge request performance guides as completed

marked the task Branch has no merge conflicts with master (if it does - rebase it please) as completed

marked the task Conform by the style guides as completed

assigned to @DouweM

merged

mentioned in commit 87b01636

mentioned in commit 33227197

Picked into 8-15-stable, will go into 8.15.0-rc4

removed ~149423 label

mentioned in merge request !19961 (merged)