rustdoc: add two regression tests #130173
                
     Merged
            
            
          
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They were basically copy/pasted from
tests/ui/totests/rustdoc-ui/.Not sure if it's worth adding these, I can just close these issues as is if you want.
This brings the number of T-rustdocRelevant to the rustdoc team, which will review and decide on the PR/issue. 
 + 
  E-needs-test
  Call for participation: An issue has been fixed and does not reproduce, but no test has been added. 
 from 3 down to 1.
The remaining one – #103004 — is a nasty one to retroactively find a proper(!) test for.
Fixes #98250.
Fixes #107872.
r? rustdoc