content test [nfc]: Pull out an expectedText variable from ContentExample

Author: chrisbobbe

test/widgets/content_test.dart

@@ -1035,11 +1035,12 @@ void main() {
       assert(ContentExample.mathInlineUnknown.html.endsWith('</p>'));
       final unsupportedKatexHtml = ContentExample.mathInlineUnknown.html
         .substring(3, ContentExample.mathInlineUnknown.html.length - 4);
+      final expectedText = ContentExample.mathInlineUnknown.expectedText!;
 
       testWidgets('maintains font-size ratio with surrounding text, when falling back to TeX source', (tester) async {
         await checkFontSizeRatio(tester,
           targetHtml: unsupportedKatexHtml,
-          targetFontSizeFinder: mkTargetFontSizeFinderFromPattern(r'\lambda'));
+          targetFontSizeFinder: mkTargetFontSizeFinderFromPattern(expectedText));
       });
     });
   });