cicd: backport: Fix events allowing the workflow to run
cicd: backport: Fix events allowing the workflow to run

Even when using pull_request_target, the merged is issued as
pull_request and this should be used to ensure we can run the workflow.

Signed-off-by: Vinicius Aquino <f9441e563c18eb5d22d487c636eb39509807b77d@ossystems.com.br>

UpdateHub/meta-updatehub,UpdateHub/meta-updatehub,UpdateHub/meta-updatehub