[NFC] Reformat sentence to use "infinite-width" formatting

That is consistent with rest of issue template.

Author: jieyouxu

.github/ISSUE_TEMPLATE/major_change.md

@@ -17,9 +17,7 @@ assignees: ''
 
 # Mentors or Reviewers
 
-*If you have a reviewer or mentor in mind for this work, mention them
-here. You can put your own name here if you are planning to mentor the
-work.*
+*If you have a reviewer or mentor in mind for this work, mention them here. You can put your own name here if you are planning to mentor the work.*
 
 # Process