[test/suite.ml] small fix in displaying source path

[FissoreD]

BEFORE:

executable: path/_build/install/default/bin/elpi
args: -test -I path/_build/install/default/bin/../lib/elpi/ -I path/tests/sources/ io_colon.elpi

AFTER:

executable: path/_build/install/default/bin/elpi
args: -test -I path/_build/install/default/bin/../lib/elpi/ -I path/tests/sources/io_colon.elpi

Note the absence of space before io_colon.elpi

[gares]

-I adds a path, the last argument 8s a file name. I'm ok passing the file name using a longer path, but not this way.

[FissoreD]

ah, sorry, I didn't know the command was meant to work like this.
The reason for having a whole absolute path to the file was that, while opening the log,
I would have been able to directly jump to the file via ctrl+click in vscode.