acciaccatura slur direction

[Joel C. Salomon]

What am I doing wrong here?

```
\version "2.24.0"
down = {
  \clef bass
  \slurUp
  \acciaccatura g,8 d'2 % works
  \acciaccatura d8 d'2 | % doesn't
}
\score {
  \down
}
```

Adding `\slurUp` to a redefinition of `\startAcciaccaturaMusic` works,
so why does the code above not work?

Adapted from the example in
<https://lilypond.org/doc/v2.24/Documentation/notation/special-rhythmic-concerns#Redefining-grace-note-global-defaults>:
```
startAcciaccaturaMusic = {
  <>(
  \override Flag.stroke-style = #"grace"
  \slurUp
}

stopAcciaccaturaMusic = {
  \revert Flag.stroke-style
  \slurNeutral
  <>)
}
```

-- Joel