homebrew/core is a shallow clone in Fish shell

I tried to install something using brew install and this thing pops up

Warning: homebrew/core is shallow clone. To get complete history run:
  git -C "$(brew --repo homebrew/core)" fetch --unshallow

and when I copied that thing to make it run, this happens

fish: $(...) is not supported. In fish, please use '(brew)'.
git -C "$(brew --repo homebrew/core)" fetch --unshallow
        ^

What does it means and how can I fix these things? Is there's a workaround to ignore or fix?

Additional information about my workstation:

Update 1 : It looks like I am an idiot leaving the $ there. I did try to fix it with you guys suggestions, and this what happened.

Removing the $ from the command, like so

git -C "(brew --repo homebrew/core)" fetch --unshallow

and this happens

fatal: cannot change to '(brew --repo homebrew/core)': No such file or directory

Update 2 : Also, @VonC asked me did brew --repo homebrew/core path exists by asking me to run these following line

brew --repo homebrew/core

and it comes up as this

/usr/local/Homebrew/Library/Taps/homebrew/homebrew-core

which indicates that the repository path is still valid and ready to use

Solution

Looks like I did a double oopsies.
Thanks to all comments to me that I am doing an oopsies. I appreciate it a lot.

Instead of typing

git -C "$(brew --repo homebrew/core)" fetch --unshallow

which fish does not really likes $ in that line,

use this instead :
git -C (brew --repo homebrew/core) fetch --unshallow
no $ and ".
AAAAND that's it.

Please comment if this does not help. I still doubt that really resolves this question or not lol