fix: remove memory leaks kruskal.c

[vil02]

Description of Change

There are two memory leaks in kruskal.c. This PR removes them.

References

Checklist

• Added description of change
• Relevant documentation/comments is changed or added
• PR title follows semantic commit guidelines
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• I acknowledge that all my contributions will be made under the project's license.

Notes:

Fixes memory leaks in kruskal.c.

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