Used docs_url variable in docs link

[ryanhiebert]

Trac ticket number

N/A

Branch description

Use the {{ docs_version }} template variable instead of hardcoding a link to the dev version.

Checklist

• This PR targets the main branch.
• The commit message is written in past tense, mentions the ticket number, and ends with a period.
• I have checked the "Has patch" ticket flag in the Trac system.
• I have added or updated relevant tests.
• I have added or updated relevant docs, including release notes if applicable.
• I have attached screenshots in both light and dark modes for any UI changes.

[sarahboyce]

Thank you!