Please read https://arm-software.github.io/ComputeLibrary/latest/contribution_guidelines.xhtml
Here on github we only publish a snapshot of the main development branch for each release, that's the reason why we don't accept pull requests.
Please submit your patch for review to review.mlplatform.org.
The development is structured in the following way:
Release repository: https://github.com/arm-software/ComputeLibrary
Development repository: https://review.mlplatform.org/#/admin/projects/ml/ComputeLibrary
Please report issues here: https://github.com/ARM-software/ComputeLibrary/issues