Update references of 'master' to 'main' in Deployment doc

[DavidIsrawi]

Issue
The deployments were referring to the master branch for the GitHub Pages documentation (which is now outdated)

Fix
Changed references to main

Notes
I was thinking of adding a disclaimer so people with an old repo were able to follow with master instead of main but ultimately decided not to add it. Let me know if you think we should

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[DavidIsrawi]

Let me know if there's anything else I should add for this PR! @iansu @mrmckeb

[matrush]

Thanks! Fixed in #10696