git: Parse `FETCH_HEAD` reference from output
Git servers can be configured to allow fetching objects from a provided
object ID. In this scenario, the fetched objects are only written to
FETCH_HEAD
and therefore the local reference printed in the porcelain
fetch output is FETCH_HEAD
.
When parsing references from git-fetch(1)
output, the reference is
validated. The current validation operation does not support
FETCH_HEAD
as a valid reference and consequently results in an error
being returned.
Update the porcelain fetch scanner to support git-fetch(1)
operations
requesting explicit object IDs.