[Bug]: cssnano misinterprets unquoted font name as color

[Invizory]

Bug Description

Consider the following CSS (all irrelevant properties are omitted):

@font-face {
  src: local(Noto Sans Black);
}

Here, Black is misinterpreted by cssnano as the name of the color, resulting in:

@font-face{src:local(Noto Sans #000)}

However, if one quotes a font face name, the problem disappears:

@font-face {
  src: local("Noto Sans Black");
}

The above example minifies to:

@font-face{src:local("Noto Sans Black")}

However, according to CSS Fonts Module Level 3 W3C recommendation, quotes are optional:

The syntax for a <font-face-name> is a unique font face name enclosed by "local(" and ")". The name can optionally be enclosed in quotes. If unquoted, the unquoted font family name processing conventions apply; the name must be a sequence of identifiers separated by whitespace which is converted to a string by joining the identifiers together separated by a single space.

It looks like the bug originates from postcss-colormin, which tries to minify color names within too many contexts without limiting oneself to the contexts where only colors can appear.

Maybe it's a good idea to add the following test to cssnano/packages/postcss-colormin/test/index.js and make it pass:

test(
  'should not attempt to convert unquoted font names',
  passthroughCSS('@font-face{src:local(Noto Sans Black)}')
);

Expected behaviour

@font-face{src:local(Black Font Name)}

Steps to reproduce

Minify the stylesheet provided above with cssnano playground or latest (5.1.14) version of cssnano.

Version

5.1.14

Preset

default

Environment

System:
  OS: Linux 5.15 Ubuntu 22.04.1 LTS 22.04.1 LTS (Jammy Jellyfish)
  CPU: (8) x64 Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz
  Memory: 2.37 GB / 15.40 GB
  Container: Yes
  Shell: 5.8.1 - /usr/bin/zsh