Format the whole speed test dial for the locale (#6994)

The dial already grouped its digits for the locale above 10, but below 10 it
went through toFixed, which hardcodes a dot. A German desktop therefore read
9.5 and 1.235 off the same dial, switching decimal convention halfway up the
scale.

Send both branches through the locale. A reading is a measurement rather than
interface text, so its separators follow the system's number conventions even
though the interface itself stays English.

English output is unchanged.

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>
(cherry picked from commit 9f109a7f3e)

shell/Ui/SpeedTestOverlay.qml

@@ -369,7 +369,13 @@ PanelWindow {
 
       Text {
         anchors.horizontalCenter: parent.horizontalCenter
-        text: dial.reading < 10 ? dial.reading.toFixed(1) : Math.round(dial.reading).toLocaleString(Qt.locale(), 'f', 0)
+        // Both branches go through the locale: a reading is a measurement, so
+        // its separators follow the system's number conventions rather than the
+        // interface language. toFixed would have hardcoded a dot below 10 while
+        // everything above it was already grouped for the locale.
+        text: dial.reading < 10
+          ? dial.reading.toLocaleString(Qt.locale(), 'f', 1)
+          : Math.round(dial.reading).toLocaleString(Qt.locale(), 'f', 0)
         color: root.onScrim
         font.family: root.fontFamily
         font.pixelSize: Style.font.display