Use specified output when using ConanFile.run() with bash

[taoyouh]

Fix #5670, #11076

Changelog: Feature: Use output provided by user when calling self.run() with win_bash=True
Docs: conan-io/docs#2543

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[memsharded]

Sorry this PR was not managed back then, it seems that the incomplete CI didn't help.
Conan 2.0 has changed all that code, so this PR would be outdated, so I am closing it. Thanks very much for your contribution anyway!