fix: grammar and spacing

[crooruhe]

Why:

Was reading documentation for oauth and ran across some confusing language
Fixes grammar and spacing

Closes:
N/A

What's being changed (if available, include any code snippets, screenshots, or gifs):

Fixes grammar/spacing in liquid template tag

Check off the following:

• A subject matter expert (SME) has reviewed the technical accuracy of the content in this PR. In most cases, the author can be the SME. Open source contributions may require a SME review from GitHub staff.
• The changes in this PR meet the docs fundamentals that are required for all content.
• All CI checks are passing.

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Content directory changes

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Source	Preview	Production	What Changed
apps/oauth-apps/building-oauth-apps/authenticating-to-the-rest-api-with-an-oauth-app.md	fpt ghec ghes@ 3.15 3.14 3.13 3.12 3.11 3.10	fpt ghec ghes@ 3.15 3.14 3.13 3.12 3.11 3.10	from reusable

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fpt: Free, Pro, Team
ghec: GitHub Enterprise Cloud
ghes: GitHub Enterprise Server

[nguyenalex836]

@crooruhe Thanks so much for opening a PR with this fix! I'll update the branch and get this merged once tests are passing 🍏

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