🐛 remove 3 backticks messing the hover (#12273)

# Description

The hover was bugged with 3 backticks. I don't understand how it worked
before, but this apparently now works correctly on my machine. This is
really puzzling. My next step is to make a test to assert this will
break a little less. I fixed it 3 times in the past

# Tests + Formatting

Added a test to be sure this doesn't breaks again 😄 (at least from
nushell/nushell side)

tests/fixtures/lsp/hover/command.nu

@@ -2,3 +2,5 @@
 def hello [] {}
 
 hello
+
+[""] | str join