`dircolors` matching should treat `^` like `!`

[ackerleytng]

Difference in behavior from GNU dircolors:

$ echo 'TERM [^a]bc\n.term_matching 00;38;5;61' | TERM=abc dircolors -b -
zsh: can't find terminal definition for abc
LS_COLORS='';
export LS_COLORS
$ echo 'TERM [!a]bc\n.term_matching 00;38;5;61' | TERM=abc dircolors -b -
zsh: can't find terminal definition for abc
LS_COLORS='';
export LS_COLORS
$ echo 'TERM [!a]bc\n.term_matching 00;38;5;61' | TERM=abc ~/projects/coreutils/uutils/target/debug/coreutils dircolors -b -
zsh: can't find terminal definition for abc
LS_COLORS='';
export LS_COLORS
$ echo 'TERM [^a]bc\n.term_matching 00;38;5;61' | TERM=abc ~/projects/coreutils/uutils/target/debug/coreutils dircolors -b -
zsh: can't find terminal definition for abc
LS_COLORS='*.term_matching=00;38;5;61:';
export LS_COLORS

I'll work on this!