Systematically test ports

[m-kuhn]

For different triplets and with systematic detection of available ports, controlled by a blocklist.
Ideally code from upstream can be reused, see https://github.com/microsoft/vcpkg/blob/master/scripts/azure-pipelines/test-modified-ports.ps1 / ci.baseline.txt.

[Neumann-A]

Have you tested if https://github.com/open-vcpkg/python-registry/blob/main/ports/vcpkg-python-scripts/import_test.py.in can fail? I had a weird issues while testing stuff like that that the script never seems to fail.

[m-kuhn]

At some point during #3 it failed, but maybe in an older version

[Neumann-A]

Would be good to have an explicitly failing test to make sure the test actual works both ways.

[Neumann-A]

From microsoft/vcpkg#37409 I noticed that the import test should only run for native builds.

[Neumann-A]

The import test script should probably be moved into the python3 port.