mergify: enable it only for feature-mergify
mergify: enable it only for feature-mergify

This will be reverted once mergify works with the PR workflow.
One rule for each condition - base is feature-mergify.

mbedmicro/mbed,mbedmicro/mbed,andcor02/mbed-os,mbedmicro/mbed,kjbracey-arm/mbed,kjbracey-arm/mbed,kjbracey-arm/mbed,andcor02/mbed-os,andcor02/mbed-os,mbedmicro/mbed,kjbracey-arm/mbed,andcor02/mbed-os,mbedmicro/mbed,andcor02/mbed-os,andcor02/mbed-os