update exiv2

[PeterPetrik]

required by qgis/QGIS#41777 (comment)

CC @nyalldawson

[PeterPetrik]

we have https://github.com/qgis/QGIS-Mac-Packager/blob/master/qgis_deps/recipes/exiv2/recipe.sh
version 0.27.2 from 2019-07-29

looks like in last tagged version 0.27.3, the problem still persists https://github.com/Exiv2/exiv2/blob/194bb65ac568a5435874c9d9d73b1c8a68e4edec/include/exiv2/value.hpp#L63

on master it is fixed

[3nids]

next release is planned on May: Exiv2/exiv2#1462

[3nids]

could this be easily patched?
otherwise, we could switch to master (exiv) that we release in a dev version of the mac-deps to use in QGIS master CI ?

[clanmills]

Please don't use the master branch of exiv2. It has been renamed 'old-master' and will be retained as it holds valuable code that we don't wish to loose. The next release of Exiv2 is v0.27.4 and on track to ship on 2021-05-22. Exiv2/exiv2#1018 (comment)

After that, we will create the 'main' from the 0.27-maintenance branch. Exiv2 v0.28 is scheduled from main on 2021-09-15.
Exiv2/exiv2#1466 (comment)