tests/lib/conds: change `nameSuffix` type to `bt2c::CStringView`

tests/lib/conds: change `nameSuffix` type to `bt2c::CStringView`

I'm not sure why `nameSuffix` is passed as a `const
bt2s::optional<std::string>&` currently.  `bt2c::CStringView` seems like
a good fit for it.  It avoids unnecessarily creating `std::string`s when
the caller passes a literal string.

Change-Id: I1412b77223fe01a70dda4c23558983f84dfb07d4
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/12114
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Tested-by: jenkins <jenkins@lttng.org>