Tests: Recognise a vmlinux subdirectory under the ported selftests

Ports of kernel selftests live in tests/passing_tests/selftests/. Those that
import from vmlinux need the same treatment as tests/passing_tests/vmlinux/ --
skipped, not failed, when no vmlinux.py has been generated for the running
kernel. Without this they fail outright on any machine lacking one, CI included.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: r41k0u

tests/framework/collector.py

@@ -7,7 +7,10 @@
 TESTS_DIR = Path(__file__).parent.parent
 CONFIG_FILE = TESTS_DIR / "test_config.toml"
 
-VMLINUX_TEST_DIRS_PASSING = {"passing_tests/vmlinux"}
+VMLINUX_TEST_DIRS_PASSING = {
+    "passing_tests/vmlinux",
+    "passing_tests/selftests/vmlinux",
+}
 VMLINUX_TEST_DIRS_FAILING = {
     "failing_tests/vmlinux",
     "failing_tests/xdp",