💄 (grapher) pass numeric slider values when possible

packages/@ourworldindata/grapher/src/timeline/TimelineComponent.tsx

@@ -455,17 +455,18 @@ const TimelineHandle = ({
     onBlur?: React.FocusEventHandler<HTMLDivElement>
 }): JSX.Element => {
     return (
-        // @ts-expect-error aria-value* fields expect a number, but we're passing a string
+        // @ts-expect-error aria-value* fields expect a number, but if we're dealing with daily data,
+        // the numeric representation of a date is meaningless, so we pass the formatted date string instead.
         <div
             className={classNames("handle", type)}
             style={{
                 left: `${offsetPercent}%`,
             }}
             role="slider"
             tabIndex={0}
-            aria-valuemin={formattedMinTime}
-            aria-valuenow={formattedCurrTime}
-            aria-valuemax={formattedMaxTime}
+            aria-valuemin={castToNumberIfPossible(formattedMinTime)}
+            aria-valuenow={castToNumberIfPossible(formattedCurrTime)}
+            aria-valuemax={castToNumberIfPossible(formattedMaxTime)}
             aria-label={label}
             onFocus={onFocus}
             onBlur={onBlur}
@@ -489,3 +490,11 @@ const TimelineHandle = ({
         </div>
     )
 }
+
+function castToNumberIfPossible(s: string): string | number {
+    return isNumber(s) ? +s : s
+}
+
+function isNumber(s: string): boolean {
+    return /^\d+$/.test(s)
+}