github: workaround release events types

Detecting the branch with GITHUB_REF doesn't work well for release GITHUB_EVENT_TYPE, because the value contains the tag. A tag might be equal to "0.2.0" for a branch "0.2". Which confuses the version checker as it keeps looking for a 0.2.0 release branch which doesn't exists.

To work around this, assume in case of a release event type, that the tag_name=branch.$micro