cubicweb-vcsfile #3579417 revision should not be updatable [validation pending]

It does not make much sense to allow a revision to be modified as it is in practice imported from the underlying vcs.

prioritynormal
typebug
done in1.15.0
load0.100
load left0.000
closed by#e45c6bd4c1a9 Disallow update of Revision entities and obsoletes relation (closes #3579417)
patchDisallow update of Revision entities and obsoletes relation (closes #3579417) [applied]