fix: markdown formatting mistake in CONTRIBUTING.md file

[Sachin Dapkara]

Description
I noticed a markdown formatting mistake in the CONTRIBUTING.md file. The mistake relates to the markdown link syntax, and it impacts the readability and usability of the document.

Specifically, the link to the compatible Flutter SDK versions is mentioned using inline code formatting, which may lead to confusion for users trying to access the link. Additionally, the URL in the link is not correctly formatted.

Screenshots

[Sachin Dapkara]

Hello,
I would like to contribute by working on this issue. So could you please consider assigning this issue to me?

Thank you,