cylc install from different source directory claims to have failed despite still copying the files #6786
Description
Reproducible Example
$ cd ~/cylc-src
$ cylc install thing
INSTALLED thing/run1 from ~/cylc-src/thing
$ ls ~/cylc-run/thing
_cylc-install run1 runN
$ cd ~/Documents/thing
$ cylc install
WorkflowFilesError: Failed to install from ~/Documents/thing: previous installations were from ~/cylc-src/thing
$ ls ~/cylc-run/thing
_cylc-install run1 run2 runNExpected Behaviour
run2 should not be created