Use python3 in tests Some upstream tests call the python interpreter in a subprocess, e.g. to test the custom `process` module or to run simple in-toto step or inspection commands. In debian, where we only build for python3, "python" is not available during build and thus makes those tests fail. This patch replaces "python" with "python3" where applicable.
diff --git a/tests/demo_files/demo.layout.template b/tests/demo_files/demo.layout.template index 64ca250..0ac7f7e 100644
