Installation request for symfony/event-dispatcher (locked at v5.1.5) -> satisfiable by symfony/event-dispatcher[v5.1.5]

composer require graze/parallel-process
Using version ^0.8.1 for graze/parallel-process
./composer.json has been updated
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Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

Problem 1
- Conclusion: remove symfony/console v5.1.5
- Conclusion: don't install symfony/console v5.1.5
- symfony/event-dispatcher 2.8.x-dev conflicts with symfony/console[v5.1.5].
- symfony/event-dispatcher v2.8.0 conflicts with symfony/console[v5.1.5].
- symfony/event-dispatcher v2.8.0-BETA1 conflicts with symfony/console[v5.1.5].
- symfony/event-dispatcher v2.8.1 conflicts with symfony/console[v5.1.5].
- symfony/event-dispatcher v2.8.10 conflicts with symfony/console[v5.1.5].
- symfony/event-dispatcher v2.8.11 conflicts with symfony/console[v5.1.5].
- symfony/event-dispatcher v2.8.12 conflicts with symfony/console[v5.1.5].
- symfony/event-dispatcher v2.8.13 conflicts with symfony/console[v5.1.5].
- symfony/event-dispatcher v2.8.14 conflicts with symfony/console[v5.1.5].
- symfony/event-dispatcher v2.8.15 conflicts with symfony/console[v5.1.5].
- symfony/event-dispatcher v2.8.16 conflicts with symfony/console[v5.1.5].
- symfony/event-dispatcher v2.8.17 conflicts with symfony/console[v5.1.5].
- symfony/event-dispatcher v2.8.18 conflicts with symfony/console[v5.1.5].