Fix transparent verification checkmark in dark mode (#30235)

* Fix transparent verification checkmark in dark mode

Fixes Issue https://github.com/element-hq/element-web/issues/28285

* Add white background to E2E Warning Icon

Also adapted the testcases to the new background.

src/components/views/rooms/E2EIcon.tsx

@@ -76,7 +76,17 @@ const E2EIcon: React.FC<Props> = ({
     if (onClick) {
         content = <AccessibleButton onClick={onClick} className={classes} style={style} />;
     } else {
-        content = <div className={classes} style={style} />;
+        // Verified and warning icon have a transparent cutout, so add a white background.
+        // The normal icon already has the correct shape and size, so reuse that.
+        if (status === E2EStatus.Verified || status === E2EStatus.Warning) {
+            content = (
+                <div className={classes} style={style}>
+                    <div className="mx_E2EIcon_normal" />
+                </div>
+            );
+        } else {
+            content = <div className={classes} style={style} />;
+        }
     }
 
     if (!e2eTitle || hideTooltip) {