DOC: Fix Typographical Error in Contributing Guidelines

[abhishekshah5486]

Issue with current documentation:

The contributing guidelines for PyTensor contain a minor typographical error. Specifically, the phrase:

"pseudocode may be acceptable, but an PyTensor implementation is always preferable"

should be corrected to:

"pseudocode may be acceptable, but a PyTensor implementation is always preferable."

This change is necessary to correct the grammatical error and ensure clarity in the documentation.

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[abhishekshah5486]

I would like work upon this issue.
Please assign it to me.
@EdwardBetts @ynd

[abhishekshah5486]

@OriolAbril
Kindly review the PR I have raised.