pbulk: add statistics for invalid dependencies to report

[Thomas Klausner <wiz%NetBSD.org@localhost>]

Hi!

I've just committed an update to the pbulk package, version 0.75.

This adds a section to text report (that is used for the emails) if
there are any packages that have invalid dependencies (i.e., which
caused pbulk to stop before my commit earlier this month).

The summary in the report now looks like this:

--- begin quote ---
Total number of packages:             18
  Successfully built:                 13
  Failed to build:                     1
  Depending on failed package:         1
  Explicitly broken or masked:         3
    of which invalid dependencies:     3
  Depending on masked package:         0
--- end quote ---

and below top breakage table there's a new table (only if any invalid
dependencies are detected, example with my (test) broken packages):

--- begin quote ---
Packages with invalid dependencies

Package                                      Location                      Maintainer
-----------------------------------------------------------------------------------------------
py311-zdist-0.0.2                            wip/py-zdist                  pkgsrc-users%NetBSD.org@localhost
py311-ydist-0.0.2                            wip/py-ydist                  pkgsrc-users%NetBSD.org@localhost
py313-zdist-0.0.2                            wip/py-zdist                  pkgsrc-users%NetBSD.org@localhost
--- end quote ---

Cheers,
 Thomas