Improve the selection check in the "doesn't jump when moving selection" integration test

Locally, on Arch Linux, this integration test permafails:

```
1) Text layer Text selection using selection carets doesn't jump when moving selection
  Message:
    second selection:
        Expected '(frequently executed) bytecode sequences, records
        them, and compiles them to fast native code. We call such a s' to roughly match /frequently .* We call such a se/s.
  Stack:
        at <Jasmine>
        at UserContext.<anonymous> (file:///home/timvandermeij/Documenten/Ontwikkeling/pdf.js/Code/test/integration/text_layer_spec.mjs:521:12)
  Message:
    third selection:
        Expected '(frequently executed) bytecode sequences, records
        them, and compiles them to fast native code. We call such a s' to roughly match /frequently .* We call such a se/s.
  Stack:
        at <Jasmine>
        at UserContext.<anonymous> (file:///home/timvandermeij/Documenten/Ontwikkeling/pdf.js/Code/test/integration/text_layer_spec.mjs:529:12
```

The exact selection can differ a bit per OS/browser. In this case the
last character was consistently not selected while on other platforms it
is, so this commit fixes the issue by relaxing the regex to not consider
the final character so that the test passes if the rest matches.

Author: timvandermeij

test/integration/text_layer_spec.mjs

@@ -509,15 +509,15 @@ describe("Text layer", () => {
 
         await expectAsync(page)
           .withContext(`second selection`)
-          .toHaveRoughlySelected(/frequently .* We call such a se/s);
+          .toHaveRoughlySelected(/frequently .* We call such a s/s);
 
         await page.mouse.down();
         await moveInSteps(page, intermediateCaretPos, finalCaretPos, 20);
         await page.mouse.up();
 
         await expectAsync(page)
           .withContext(`third selection`)
-          .toHaveRoughlySelected(/frequently .* We call such a se/s);
+          .toHaveRoughlySelected(/frequently .* We call such a s/s);
       });
     });
   });