Allow to have - in rustdoc-json test file name
          #113613
        
          
      
                
     Merged
            
            
          
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I extracted this commit from #113574.
When I added the test, it kept saying that the JSON file couldn't be found. After investigating for a while, I discovered that we were expecting files to always use
_, which is quite bad. So I added support for-in file names.r? @notriddle