Consecutive keywords are not rightfully colorised

[jthulhu]

Issue description

Keywords that are only space-separated are not colorised as they should: only the first one has the keyword font, the next one has regular colorisation. Inserting a newline in between solves it.

Examples

Note how github will colorise every keyword, but in the comments I point out the ones that will not get colored by Emacs.

{
    a = let in {}; # `let` is colorized, not `in`
    b = let something = 3; in rec {}; # `rec` is not colorised
    c = let in with rec {}; 3; # `let` and `with` are colorised, not `in` and `rec`.
}

Also, in this case, it all works as in github:

{
    a = let 
        in {};
    b = let something = 3; in
        rec {};
    c = let
        in 
        with
        rec {}; 3;
}

Version

I tested this in the latest NixOS unstable version there is (at the time writing), Emacs 29.0.50 and nix-mode is version 20220505.1706 (the latest published on melpa for the time being). However, this seems like a lasting bug because I have experienced this strange behavior for some time now.