Correct grammar in pages build skipping section

[ClaytonTDM]

Summary

Corrects grammar in the pages build skipping section.

This changes the following line:

By adding the [CI Skip], [CI-Skip], [Skip CI], [Skip-CI], or [CF-Pages-Skip] flag as a prefix in your commit message, and Pages will omit that deployment.

to:

By adding the [CI Skip], [CI-Skip], [Skip CI], [Skip-CI], or [CF-Pages-Skip] flag as a prefix in your commit message, Pages will omit that deployment.

Documentation checklist

• The change adheres to the documentation style guide.