Positioning text markups inside slurs

Text markups need to have the outside-staff-priority property set to #f in order to be printed inside slurs.

\version "2.24"

\relative c'' {
  \override TextScript.avoid-slur = #'inside
  \override TextScript.outside-staff-priority = ##f
  c2(^\markup { \halign #-10 \natural } d4.) c8
}