Allure-pytest: report.longrepr information just available in allure web app if test fails with an exception

[//]: # (
. Note: for support questions, please use Stackoverflow or Gitter**.
. This repository's issues are reserved for feature requests and bug reports.
.
. In case of any problems with Allure Jenkins plugin** please use the following repository
. to create an issue: https://github.com/jenkinsci/allure-plugin/issues
.
. Make sure you have a clear name for your issue. The name should start with a capital
. letter and no dot is required in the end of the sentence. An example of good issue names:
.
. - The report is broken in IE11
. - Add an ability to disable default plugins
. - Support emoji in test descriptions
)

#### I'm submitting a ...
- [ ] bug report
- [X] feature request
- [ ] support request => Please do not submit support request here, see note at the top of this template.

#### What is the current behavior?

Allure-pytest plugin just show failure information if the test throws an exception.

https://github.com/allure-framework/allure-python/blob/5e7bc860b5ddc1e072b0302022669183f2c4321f/allure-pytest/src/listener.py#L161-L182

#### What is the motivation / use case for changing the behavior?
Some useful plugins, like [pytest-check](https://github.com/okken/pytest-check), allow a non-fatal assertion behaviour modifying "report.longrepr" variable. "report.longrepr" could be valuable to get extra information in case of fail without exception information.

#### Please tell us about your environment:

- Allure version: 2.13.8
- Test framework: pytest@6.2.2
- Allure adaptor: allure-pytest@2.8.32

Comienza en allure-pytest/src/listener.py, en las líneas 161-182, e inspecciona cómo se recopila actualmente la información de los fallos. Sigue el procesamiento de los informes de pytest para los fallos sin excepciones y, después, haz que report.longrepr esté disponible en el informe web de Allure; estará terminado cuando se muestren los detalles de aserciones no fatales de plugins como pytest-check.

Escrito por el modelo de indexación a partir del texto del issue.