Cannot install with Symfony/Yaml 5.0

[jaydiablo]

Steps to reproduce

Ran composer require consolidation/robo --dev in a project that has symfony/yaml required at ^5.0.0.

Expected behavior

Robo should install

Actual behavior

Robo fails installation:

Problem 1
    - Conclusion: don't install symfony/yaml 4.4.x-dev
    - Conclusion: don't install consolidation/robo 2.1.0
    - Conclusion: remove symfony/translation v5.1.0
    - Installation request for symfony/yaml (locked at v5.1.0, required as ^5.1.0) -> satisfiable by symfony/yaml[v5.1.0].
    - Installation request for consolidation/robo ^2.1 -> satisfiable by consolidation/robo[2.1.0, 2.x-dev].
    - Conclusion: don't install symfony/translation v5.1.0
    - consolidation/robo 2.x-dev requires grasmash/yaml-expander ^1.4 -> satisfiable by grasmash/yaml-expander[1.4.0, 1.x-dev].
    - grasmash/yaml-expander 1.4.0 requires symfony/yaml ^2.8.11|^3|^4 -> satisfiable by symfony/yaml[2.8.x-dev, 3.0.x-dev, 3.1.x-dev, 3.2.x-dev, 3.3.x-dev, 3.4.x-dev, 4.0.x-dev, 4.1.x-dev, 4.2.x-dev, 4.3.x-dev, 4.4.x-dev].
    - grasmash/yaml-expander 1.x-dev requires symfony/yaml ^2.8.11|^3|^4 -> satisfiable by symfony/yaml[2.8.x-dev, 3.0.x-dev, 3.1.x-dev, 3.2.x-dev, 3.3.x-dev, 3.4.x-dev, 4.0.x-dev, 4.1.x-dev, 4.2.x-dev, 4.3.x-dev, 4.4.x-dev].

This appears to be because of the grasmash/yaml-expander dependency: https://github.com/consolidation/Robo/blob/master/composer.json#L30

The 1.x line of grasmash/yaml-expander requires symfony/yaml ^2.8.11|^3|^4: https://github.com/grasmash/yaml-expander/blob/1.4.0/composer.json#L7

The 2.x line still doesn't bump to symfony/yaml 5.0 though: https://github.com/grasmash/yaml-expander/blob/2.0.0/composer.json#L9

Have to allow 3.0.0 so that symfony/yaml 5.0 will be allowed: https://github.com/grasmash/yaml-expander/blob/3.0.0/composer.json#L8

Related to #917

System Configuration

PHP 7.3.18