Fixed unused variable code action

[scohen]

The quote character around the variable name was changed, this broke the code action for replace unused variables.

[scottming]

The initial reason for making this change was that I thought using backticks for the token aligns better with markdown syntax, indicating it's part of the code. This will be advantageous for editors supporting treesitter.

More importantly, I find that compared to ", backticks are easier on the eyes to recognize, as " can be disruptive to identify. You can see the comparison in the following few images:

editor	"	backtick
nvim
vscode

[scohen]

How is it advantageous for a treesitter based editor? Diagnostics aren't part of the code, and aren't displayed via markdown.