Tests: Register a vmlinux subdirectory under kernel_selftest_equivalent

Ports 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 wherever one
is absent, 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",
+    "kernel_selftest_equivalent/vmlinux",
+}
 VMLINUX_TEST_DIRS_FAILING = {
     "failing_tests/vmlinux",
     "failing_tests/xdp",