Fix unit tests

[soininen]

A unit test got broken due to changes in spine-engine.

Re spine-tools/spine-engine#99

Checklist before merging

• [x] Documentation (also in Toolbox repo) is up-to-date
• [x] Release notes in Toolbox repo have been updated
• [x] Unit tests have been added/updated accordingly
• [x] Code has been formatted by black
• [ ] Unit tests pass

[codecov-commenter]

Codecov Report

Patch coverage has no change and project coverage change: -0.01 :warning:

Comparison is base (05a7e8a) 54.74% compared to head (d9f1971) 54.73%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #128 +/- ## ========================================== - Coverage 54.74% 54.73% -0.01% ========================================== Files 192 192 Lines 17319 17319 Branches 2838 2838 ========================================== - Hits 9481 9480 -1 Misses 7349 7349 - Partials 489 490 +1 ``` [see 1 file with indirect coverage changes](https://app.codecov.io/gh/spine-tools/spine-items/pull/128/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spine-tools)

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