TEST-06-SELINUX: Only enable if meson was invoked as root

This test only works if the image was built as root. Since that's
impossible to check as meson generally runs before we build the image,
let's use whether meson is run as root as a proxy.

test/integration-tests/TEST-06-SELINUX/meson.build

@@ -1,5 +1,8 @@
 # SPDX-License-Identifier: LGPL-2.1-or-later
 
+id = find_program('id', required : true)
+uid = run_command(id, '-u', check : true).stdout().strip().to_int()
+
 integration_tests += [
         integration_test_template + {
                 'name' : fs.name(meson.current_source_dir()),
@@ -11,5 +14,6 @@ integration_tests += [
                 # Make sure we don't mount anything with virtiofs as otherwise fixfiles will try to relabel
                 # it.
                 'mkosi-args' : integration_test_template['mkosi-args'] + ['--runtime-build-sources=no'],
+                'enabled' : uid == 0,
         },
 ]