[DRE-maint] Bug#991245: diaspora fails to handle triggers in postinst

[Pirate Praveen]

Package: diaspora
Version: 0.7.15.0-7
severity: grave

Processing triggers for diaspora (0.7.15.0-7~bpo11+1) ...
Updating bundler configuration for migration from diaspora-installer...
postinst called with unknown argument `triggered'
dpkg: error processing package diaspora (--configure):
 installed diaspora package post-installation script subprocess 
returned error exit status 1
Processing triggers for libc-bin (2.31-12) ...
Errors were encountered while processing:
 diaspora

postinst script should be adapted to handle this case like gitlab does 
in

https://salsa.debian.org/ruby-team/gitlab/-/blob/master/debian/gitlab.postinst#L342

and 
https://salsa.debian.org/ruby-team/gitlab/-/blob/master/debian/gitlab.postinst#L82