extended verification for git tags - as-installed tests

 git-evtag can be used as a replacement for git-tag -s. It will
 generate a strong checksum (called Git-EVTag-v0-SHA512) over
 the commit, tree, and blobs it references (and recursively over
 submodules).
 .
 This package contains "as-installed" automated tests, typically used via
 gnome-desktop-testing-runner or autopkgtest.