Fix typo in project-level overview section

[Bharat34816]

What are you changing in this pull request and why?

Checklist

• The changes in this PR meet the docs style guide/fundamentals required for all content.
• Applied the proper versioning rules if the content is for specific dbt version(s): (version a whole page or version a block of content
• The content in this PR requires a dbt release note, so I added one to the release notes page.).

[vercel]

@Bharat34816 is attempting to deploy a commit to the dbt-labs Team on Vercel.

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[luna-bianca]

Thanks for the contribution, @Bharat34816!

The heading currently reads "Custom project-level overviews" (plural), and that matches the content correctly. The section explains that you can set a different overview for each dbt project/package. Changing it to singular "overview" would make the heading inconsistent with the text underneath it.

Closing this PR for now -- happy to look at other typo fixes if you spot them elsewhere in the docs!