diag.t: Use correct variable

diag.t: Use correct variable

Multiline messages are listed in the __DATA__ section with spaces
instead of line breaks.  When adding proper support for multiline err-
ors earlier, I made a slight mistake and caused multiline to-do mess-
ages to skip the to-do code path, because I was looking them up via
the name with line breaks ($name), rather than the name with line
breaks modified ($key).

This was causing it to fall down to the pass($key) below.

I want to add more tests down there, which will fail for multiline
to-do items.