Fix flaky spec in `namespace_projects_resolver_spec`

What does this MR do and why?

note: I was never able to reproduce this flaky failure locally.

Context

When I look through the code, it looks like this spec is relying on two assumptions:

1. the gids of the FactoryBot created projects are created in the same sequential order they are defined in the code
2. Project.all will always return these projects in the same order

I think those two assumptions are possibly the root cause.

In the Namespace::ProjectsFinder we end up calling sort_by_attribute(:similarity)

def sort(items)
  return items.projects_order_id_desc unless params[:sort]

  if params[:sort] == :similarity && params[:search].present?
    return items.sorted_by_similarity_desc(params[:search])
  end

  # We end up here with `params[:sort]` == :similarity
  items.sort_by_attribute(params[:sort])
end

This eventually falls through to the sortable concern. As :similarity isn't a column or globally defined search, it falls back to the all scope:

def order_by(method)
  simple_sorts.fetch(method.to_s, -> { all }).call
end

Because of this default, the resulting query has no explicit ORDER BY clause, which conflicts with the specs assumption of some sort of order

generated SQL

SELECT
    "projects"."id",
    "projects"."name",
    "projects"."path",
    "projects"."description",
    "projects"."created_at",
    "projects"."updated_at",
    "projects"."creator_id",
    "projects"."namespace_id",
    "projects"."last_activity_at",
    "projects"."import_url",
    "projects"."visibility_level",
    "projects"."archived",
    "projects"."avatar",
    "projects"."merge_requests_template",
    "projects"."star_count",
    "projects"."merge_requests_rebase_enabled",
    "projects"."import_type",
    "projects"."import_source",
    "projects"."approvals_before_merge",
    "projects"."reset_approvals_on_push",
    "projects"."merge_requests_ff_only_enabled",
    "projects"."issues_template",
    "projects"."mirror",
    "projects"."mirror_last_update_at",
    "projects"."mirror_last_successful_update_at",
    "projects"."mirror_user_id",
    "projects"."shared_runners_enabled",
    "projects"."runners_token",
    "projects"."build_allow_git_fetch",
    "projects"."build_timeout",
    "projects"."mirror_trigger_builds",
    "projects"."pending_delete",
    "projects"."public_builds",
    "projects"."last_repository_check_failed",
    "projects"."last_repository_check_at",
    "projects"."only_allow_merge_if_pipeline_succeeds",
    "projects"."has_external_issue_tracker",
    "projects"."repository_storage",
    "projects"."repository_read_only",
    "projects"."request_access_enabled",
    "projects"."has_external_wiki",
    "projects"."ci_config_path",
    "projects"."lfs_enabled",
    "projects"."description_html",
    "projects"."only_allow_merge_if_all_discussions_are_resolved",
    "projects"."repository_size_limit",
    "projects"."printing_merge_request_link_enabled",
    "projects"."auto_cancel_pending_pipelines",
    "projects"."service_desk_enabled",
    "projects"."cached_markdown_version",
    "projects"."delete_error",
    "projects"."last_repository_updated_at",
    "projects"."disable_overriding_approvers_per_merge_request",
    "projects"."storage_version",
    "projects"."resolve_outdated_diff_discussions",
    "projects"."remote_mirror_available_overridden",
    "projects"."only_mirror_protected_branches",
    "projects"."pull_mirror_available_overridden",
    "projects"."jobs_cache_index",
    "projects"."external_authorization_classification_label",
    "projects"."mirror_overwrites_diverged_branches",
    "projects"."pages_https_only",
    "projects"."external_webhook_token",
    "projects"."packages_enabled",
    "projects"."merge_requests_author_approval",
    "projects"."pool_repository_id",
    "projects"."runners_token_encrypted",
    "projects"."bfg_object_map",
    "projects"."detected_repository_languages",
    "projects"."merge_requests_disable_committers_approval",
    "projects"."require_password_to_approve",
    "projects"."max_pages_size",
    "projects"."max_artifacts_size",
    "projects"."pull_mirror_branch_prefix",
    "projects"."remove_source_branch_after_merge",
    "projects"."marked_for_deletion_at",
    "projects"."marked_for_deletion_by_user_id",
    "projects"."autoclose_referenced_issues",
    "projects"."suggestion_commit_message",
    "projects"."project_namespace_id",
    "projects"."hidden",
    "projects"."organization_id"
FROM
    "projects"
WHERE
    "projects"."namespace_id" = 2

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Related to #446251 (closed)