less.nix: fix escape

[kvtb]

$$ does not escape $
\$ does

[kvtb]

That raises the question: when are those examples from mkOption evaluated?
I expected they are used to produce the documentation, but this bug proves that they are never evaluated (the evaluation fails because there is in fact no my-configs in pkgs)
Should they be removed?
Just for code brevity.
There are 10000s lines of them

[sternenseemann]

These are evaluated when building the nixos manual like this for example: nix-build nixos/release.nix -A manual.

The current situation constitutes no eval error at least "$${foo}" evaluate to $${foo} interestingly enough, but the strings are wrong and should be fixed.

[sternenseemann]

For reference, here you can observe the issue in the wild.

[kvtb]

wow. then there is a bug in syntax highlighting of my editor

[sternenseemann]

Nix escaping rules are pretty quirky, so I'd expect most syntax highlighters are not 100% accurate.