Optimize issue number in PR template

Author: CodeCasterX

.github/PULL_REQUEST_TEMPLATE.md

@@ -25,7 +25,7 @@ Do not create a Pull Request without creating an issue first.
 <!-- 请先创建 Issue 讨论，然后在这里链接 -->
 <!-- Please create an issue for discussion first, then link it here -->
 
-**Issue 链接 / Issue Link:** #{$IssueNumber} 👈👈
+**Issue 链接 / Issue Link:** <mark>#{$IssueNumber}</mark> 👈👈
 
 <!-- 请修改 {$IssueNumber} 为真实的编号。 -->
 <!-- Please update {$IssueNumber} to an actual number. -->