Fix wrong face attribute of box attribute.

[ayatakesi]

Hello,

I instalked recent commit and try M-x slack-start, I got bellow error.

set-face-attribute: Invalid face box: :line-width, 1, :style, released-button, :foreground, "#2aa198"

This error occured due to wrong attribute :foreground. After correct specifying :color instead of :foreground, this error seems fixed.

Thanks.

[sleep-walker]

It seems, @isamert, that you're collecting open pull requests aleady, would you mind picking this up as well? it seems to be problem for Emacs 30. TIA

[isamert]

I'm not on Emacs 30 but I guess the patch also works on 29. Applied it, thanks for the heads up.

[ag91]

I think this got merged via @isamert repository, thanks for your fix @ayatakesi . Please reopen if you the latest version still has the problem :sunny: