fix: replace broken collation comparison level link

[latonis]

DESCRIPTION

Update "ICU Comparison Levels" hyperlink to the correct, non-broken link

STAGING

N/A I assume as not a MongoDB employee?

JIRA

N/A I assume as not a MongoDB employee?

Self-Review Checklist

• [x] Is this free of any warnings or errors in the RST?
• [x] Is this free of spelling errors?
• [x] Is this free of grammatical errors?
• [x] Is this free of staging / rendering issues?
• [x] Are all the links working?

External Review Requirements

What's expected of an external reviewer?