fix(docs): correct md link syntax in HISTORY.md

[nedbat]

Change Summary

Three links in HISTORY.md weren't correct Markdown syntax.

Checklist

• The pull request title is a good summary of the changes - it will be used in the changelog
• Unit tests for the changes exist: NA
• Tests pass on CI
• Documentation reflects the changes where applicable: NA
• My PR is ready to review, please add a comment including the phrase "please review" to assign reviewers

Selected Reviewer: @davidhewitt

[nedbat]

please review

[codspeed-hq]

CodSpeed Performance Report

Merging #9530 will not alter performance

_{Comparing nedbat:patch-1 (04d7c03) with main (1f47473)}

Summary

✅ 13 untouched benchmarks

[sydney-runkle]

Thank you!!

[nedbat]

@sydney-runkle btw, I hear "welcome to Boston" is in order :) https://about.bostonpython.com

[sydney-runkle]

@nedbat, indeed, thanks! I'm excited to move this coming fall. I'll certainly be attending some Boston Python events :).