Use <div> tag instead of <a> tag when no newer-post exists

[markruler]

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Currently, the <a> tag is being used even when there are no newer posts in the list. Since no link is necessary in such cases, I replaced the <a> tag with a <div> tag.

Please review my PR. @AmazingRise

https://pagespeed.web.dev/ -> https://markruler.github.io/posts/os/swap-memory/