podcheck.t: Extract line numbers from strings properly

podcheck.t: Extract line numbers from strings properly

There was a typo in this regex.  I added a \b for good measure.
This bug was currently showing up on VMS-only, where a string
was getting returned instead of a hash.  And the regex that
deals with strings had a typo, so wasn't matching.

It remains to be seen if there is an underlying issue on VMS that
was causing this error, and other OSs don't have it.