Active Record Associations lesson: Fix grammar and spelling

[jambalong]

Correct grammar and spelling: "is assume" to "is to assume" and "Often times" to "Oftentimes"

Because

This pull request addresses grammatical errors and spelling inconsistencies in the active_record_associations.md file. Specifically, it corrects "is assume" to "is to assume" for improved clarity and changes "Often times" to "Oftentimes" to ensure proper usage. These updates enhance the readability and professionalism of the lesson, making it easier for readers to understand the material.

This PR

• Changes "is assume" to "is to assume" for grammatical correctness.
• Replaces "Often times" with "Oftentimes" to adhere to proper spelling conventions.

Issue

Closes #XXXXX

Additional Information

Pull Request Requirements

• I have thoroughly read and understand The Odin Project curriculum contributing guide
• The title of this PR follows the location of change: brief description of change format, e.g. Intro to HTML and CSS lesson: Fix link text
• The Because section summarizes the reason for this PR
• The This PR section has a bullet point list describing the changes in this PR
• If this PR addresses an open issue, it is linked in the Issue section
• If any lesson files are included in this PR, they have been previewed with the Markdown preview tool to ensure it is formatted correctly
• If any lesson files are included in this PR, they follow the Layout Style Guide

[JoshDevHub]

Thanks for making this PR @jambalong 🙌

While we're in this file, there are formatting errors with the codeblocks in this lesson. This wasn't anything you did, but before I merge, would you be okay fixing them?

Codeblocks should use 3 backtick characters ``` instead of 3 tilde characters ~~~. If you don't want to fix it, that's okay and I can go ahead and merge this as is. Just figured since we're already working on this file, we could potentially get that cleaned up as well. Let me know your preference.

[jambalong]

@JoshDevHub
I have committed the fixes to the formatting errors for all code blocks in the lesson. The 3 tilde characters should now be replaced with 3 backtick characters to properly render the code snippets.

[JoshDevHub]

Thank you for fixing that little problem. There are some other errors in this file that somehow weren't caught on first pass, but I don't want to make you fix things twice. So I'll just merge this.

Thank you for contributing.