Add upstream tests as autopkgtests

Install upstream tests at /usr/libexec/installed-tests/gcr4/ and use them for testing the various libraries provided by this source package.

The test programs either link against the provided libraries, or they include the same compiled source code as a library in case of static or derived libraries.

I haven't forgotten about this merge request but I'm checking with Seb on how we want to handle this since this is a fairly complex change.

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• 62c22750...110ae00f - 114 commits from branch gnome-team:debian/latest
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• d6de9a9e - Update British English translation
• 996bdd3e - ci: Disable container building
• d5f5d29b - gcr: Support parsing ed25519 SSH public keys
• de00168b - Release stable version 4.4.0
• 90699a44 - Release stable 4.4.0.1
• dff3c434 - New upstream version 4.4.0.1
• a4b808a1 - Update upstream source from tag 'upstream/4.4.0.1'
• 117d8c45 - New upstream release
• fd391669 - changelog
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Cleaned this up now that I got more experience

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