.mergify/config.yml: Explicitly set reporting_method to check-runs

The default value of merge_protections_settings.reporting_method is
changing from check-runs to deployments. This commit updates the
mergify configuration to explicitly set check-runs to preserve
current behavior.

(deadline: 2026-07-31)

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This was originally auto-generated by the Mergify bot in a PR to the
edk2 repo. That change did not comply with edk2 commit requirements
and modified the line endings of the file. It is manually recreated
here with the correct line endings and commit message format.

Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>