Update knight_tour.py

[yuvashrikarunakaran]

Function Renaming:

Changed get_valid_pos to get_valid_moves for clarity.

Describe your change:

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
• Documentation change?

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[algorithms-keeper]

Closing this pull request as invalid

@yuvashrikarunakaran, this pull request is being closed as none of the checkboxes have been marked. It is important that you go through the checklist and mark the ones relevant to this pull request. Please read the Contributing guidelines.

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