This is a strange one because it should be possible, but I think there is something unusual with caching on the Mastodon side, where Mastodon does not re-check a blog for whether it’s verified.
However, it does require a little set up first. The easiest way is to install the “Meta tags” plug-in on Micro.blog and then enter something like the following:
If Mastodon doesn’t notice the change soon, you can also try clicking in Micro.blog → Account → Update Settings, which will tell Mastodon that you’ve made a change to your profile.
Sorry, I think I totally misunderstood your question! Apologies. My instructions were for making sure a web site on another Mastodon account is verified.
For Mastodon showing a fediverse account hosted on Micro.blog… Yeah, I don’t know why that doesn’t just work on Mastodon by default. We may need to dig into this more.