Added missing documentation in collaboration.php

[sandipr942]

What?

Closes #77172

Why?

• Added missing documentation in collaboration.php

Testing Instructions

• Open collaboration.php
• See Global documentation is missing for global $pagenow;

[github-actions]

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[shail-mehta]

in core already added missing global documentation here

[t-hamano]

Nice catch 👍

[github-actions]

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[shail-mehta]

Thank you @t-hamano for the review.

Thank you @sandipr942 for your contribution.