test-cgroup-util: ignore -ENXIO in more places

In https://github.com/systemd/systemd/pull/38003, one test failed:
Unit tests / build (CLANG_ASAN_UBSAN):
src/test/test-cgroup-util.c:237: Assertion failed: Expected "r" to succeed, but got error: No such device or address

Checks for specific errors were added in ca82f0cbe2,
partially relaxed in e92d699dde.
cg_pidref_get_unit() and cg_pid_get_slice() enter a deep chain of calls,
so it's hard to guess where the failure occurred. But those two calls
expect the cgroup path to be "well formed". When we're running in CI,
we don't have full control over what is happening on the machine,
so let's suppress that error too.

src/test/test-cgroup-util.c

@@ -234,9 +234,9 @@ TEST(proc, .sd_booted = true) {
                 r = cg_pid_get_path_shifted(pid.pid, NULL, &path_shifted);
                 ASSERT_OK_OR(r, -ESRCH);
                 r = cg_pidref_get_unit(&pid, &unit);
-                ASSERT_OK_OR(r, -ESRCH);
+                ASSERT_OK_OR(r, -ESRCH, -ENXIO);
                 r = cg_pid_get_slice(pid.pid, &slice);
-                ASSERT_OK_OR(r, -ESRCH);
+                ASSERT_OK_OR(r, -ESRCH, -ENXIO);
 
                 /* Not all processes belong to a specific user or a machine */
                 r = cg_pidref_get_owner_uid(&pid, &uid);