:bug: :white_check_mark: Fix KeyError on MemoryDataset outputs & add tests (#69)

[michal-mmm]

Description

(#69)

Development notes

What have you changed, and how has this been tested?

• used .get() on catalog._datasets to avoid KeyError
• added tests with the initial bug
• ran previously failing code (spaceflights-pandas kedro starter)

Checklist

• [x] Read the contributing guidelines
• [x] Open this PR as a 'Draft Pull Request' if it is work-in-progress
• [x] Update the documentation to reflect the code changes
• [x] Add a description of this change and add your name to the list of supporting contributions in the CHANGELOG.md file. Please respect Keep a Changelog guidelines.
• [x] Add tests to cover your changes

Notice

• [x] I acknowledge and agree that, by checking this box and clicking "Submit Pull Request":

• I submit this contribution under the Apache 2.0 license and represent that I am entitled to do so on behalf of myself, my employer, or relevant third parties, as applicable.

• I certify that (a) this contribution is my original creation and / or (b) to the extent it is not my original creation, I am authorised to submit this contribution on behalf of the original creator(s) or their licensees.

• I certify that the use of this contribution as authorised by the Apache 2.0 license does not violate the intellectual property rights of anyone else.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (e40fd99) to head (1e65a76).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #70 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 5 5 Lines 113 114 +1 ========================================= + Hits 113 114 +1 ```

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[Galileo-Galilei]

Is it ready to merge?

[michal-mmm]

Yes, it is