tests: src.ctf.fs: add test for metadata with invalid syntax

It looks like we don't have any test for a metadata file with a syntax
error in it.  Add one.

It could be argued that we should not error out in that case, as there
may be unrelated files called `metadata`, and if they don't parse as CTF
1 metadata files, we should just skip over them.  But erroring out is
the current behavior of Babeltrace 2, so it should be tested to ensure
it doesn't change by mistake.

Change-Id: I82cae8ebc5df984592205c28041276cc861f30df
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/8511
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>