self test added for kruskals minimum spanning tree

[sOR-o]

Description of Change

Added the self test cases for the greedy_algorithms/kruskals_minimum_spanning_tree.cpp issue #2509.

Checklist

• Added description of change
• Added file name matches File name guidelines
• Added tests and example, test must pass
• Added documentation so that the program is self-explanatory and educational - Doxygen guidelines
• Relevant documentation/comments is changed or added
• PR title follows semantic commit guidelines
• Search previous suggestions before making a new one, as yours may be a duplicate.
• I acknowledge that all my contributions will be made under the project's license.

[vil02]

Please note that the current implementation of the function greedy_algorithms::findMinimumEdge is not testable. What could be done to make it testable? What do you think about returning some array from it? At the moment this function displays some data - that makes it difficult to check if the result is correct.

[vil02]

It took me a while to find out what happens here.

[realstealthninja]

Suggested change

	test();
	test(); // run self-test implementations

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[github-actions]

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