Let the accessibility test see a callback that takes an argument

`sets()` recognised `name:` and `name =>` and not `name(arg) =>`, which is how
Slint writes a callback handler with a parameter. There is exactly one of those
among the properties asserted — `accessible-action-set-value`, the action a
screen reader uses to type a number into a slider — so the test reported
`SliderTrack` as missing the action it declares four lines above.

A false alarm rather than a false pass, and the less dangerous of the two. It
is still worth fixing rather than dropping the assertion: set-value is the
action that makes a slider reachable without dragging, which is most of what
the actions were added for.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

ui/dr-ui/tests/ui_controls_are_accessible.rs

@@ -180,7 +180,13 @@ fn line_offsets(source: &str) -> impl Iterator<Item = (usize, &str)> {
 }
 
 /// Whether a block sets a property — the name at the start of a line, followed
-/// by `:` for a property or `=>` for a callback.
+/// by what Slint puts after a name it is binding to.
+///
+/// Three forms, and the third is easy to forget: `name:` for a property,
+/// `name =>` for a callback, and `name(arg) =>` for a callback that takes one.
+/// `accessible-action-set-value` is the only member of the third group here and
+/// leaving it out made this test report the slider as missing the very action
+/// it declares.
 ///
 /// Anchored at the start of the trimmed line so that a *mention* in the prose
 /// above a component does not count. These files carry more comment than code,
@@ -191,8 +197,10 @@ fn line_offsets(source: &str) -> impl Iterator<Item = (usize, &str)> {
 fn sets(block: &str, property: &str) -> bool {
     block.lines().any(|line| {
         let line = line.trim_start();
-        line.strip_prefix(property)
-            .is_some_and(|rest| rest.starts_with(':') || rest.trim_start().starts_with("=>"))
+        line.strip_prefix(property).is_some_and(|rest| {
+            let rest = rest.trim_start();
+            rest.starts_with(':') || rest.starts_with("=>") || rest.starts_with('(')
+        })
     })
 }