When I attach an image diff with Attach keyword, the report comparator has the height of the shortest image

Hi everybody,

I'm using `allure-robotframework==2.15.2` with `robotframework==7.3.2`
My report is generated with allure-commandline version 2.34.1 `npx --yes allure-commandline generate`

When I attach images (diff, expected, actual) with Attach keyword, then the images displayed in "Show overlay" mode are too short. The bottom of the biggest images is hidden. I have to set the effective size of the `//div[@class="screen-diff__overlay screen-diff__container"]` to show it completely.

For example I've two images with different sizes :

- left img **2109px**
- right img **1907px**
- Comparator size **1926.9px** `//div[@class="screen-diff__overlay screen-diff__container"]`

I expect the comparator height to be at least **2109** instead of **1926**

I don't know if the issue is on allure report or in the listener allure-robotframework

Here is my snipet :
```
${dico}= Create Dictionary expected=data:image/png;base64,${expected_Base64}
... actual=data:image/png;base64,${actual_Base64} diff=data:image/png;base64,${diff_Base64}

${discoAsString} = Convert To String ${dico}
${discoAsStringDoubleQuote} Replace String ${discoAsString} ' "
${dicoAsJson} Convert String To Json ${discoAsStringDoubleQuote}
AllureLibrary.Attach ${discoAsStringDoubleQuote} name=Screenshot diff
... attachment_type=application/vnd.allure.image.diff
```

Thanks for feedback

提供された allure-robotframework、Robot Framework、allure-commandline のバージョンを使用し、高さの異なる expected、actual、diff の画像で image-diff 添付ファイルを再現する。comparator の動作が Python listener と生成されたレポートのどちらに属するのかを特定し、その後、Show overlay が最も高い画像の全高を表示することを検証する。

索引モデルが issue の本文から書いたものです。