[PATCH Search::Xapian] Makefile.PL: fix automated testing false negative

[Olly Betts]

On Sun, Sep 15, 2019 at 05:29:02PM +0000, Alyssa Ross wrote:
> In the case of Search::Xapian 1.2.x and xapian-core 1.4.y, $msg is
> deliberately unset because the two versions should be
> compatible. Since this is intended to be an escape from this
> conditional, it should be respected by the AUTOMATED_TESTING check, so
> automated testing with compatible libraries doesn't nevertheless
> result in no Makefile.

Thanks for spotting, applied in git.

Cheers,
    Olly