The install message refers to `/usr/local/share/doc/matrix-synapse/UPGRADE.rst`, however this file just contains a notice that the file has moved.
(In reply to Jaap Aarts from comment #0) Good catch! I've updated the path to the upgrade documentation and modified the reference in the patch for the 1.144.0 upgrade, see bug #292129. Thank you :)
Fixed by bug #292129.