Fix typo and indefinite article before HTTP/HTTPS

[eknathdj]

Small grammar/typo corrections (the category listed first under "Content we accept"):

• Fix misspelling "recieved" -> "received".
• Fix "a" -> "an" before "HTTP"/"HTTPS". Both are voiced with a leading vowel sound ("aitch-tee-tee-pee"), so the article is "an", matching the usage already dominant across the docs.

Prose-only edits; no code blocks, Liquid tags, or identifiers changed. These are trivial corrections, so no separate tracking issue was opened.

Pages:

• apps/oauth-apps/.../best-practices-for-creating-an-oauth-app
• pages/.../securing-your-github-pages-site-with-https (2 occurrences)
• actions/reference/github-actions-importer/supplemental-arguments-and-settings
• issues/.../automating-your-project/using-the-api-to-manage-projects

[subatoi]

Thank you for spotting this and raising a PR, @eknathdj — I'll get this merged now 🙇