selftests/bpf: Free bpf_object in test_sysctl

ASAN reported a resource leak due to the bpf_object not being tracked
in test_sysctl. Add obj field to struct sysctl_test to properly clean
it up.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Link: https://lore.kernel.org/r/20260223190736.649171-17-ihor.solodrai@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: theihor

tools/testing/selftests/bpf/prog_tests/test_sysctl.c

@@ -27,6 +27,7 @@ struct sysctl_test {
 		OP_EPERM,
 		SUCCESS,
 	} result;
+	struct bpf_object *obj;
 };
 
 static struct sysctl_test tests[] = {
@@ -1471,6 +1472,7 @@ static int load_sysctl_prog_file(struct sysctl_test *test)
 		return -1;
 	}
 
+	test->obj = obj;
 	return prog_fd;
 }
 
@@ -1573,6 +1575,7 @@ static int run_test_case(int cgfd, struct sysctl_test *test)
 	/* Detaching w/o checking return code: best effort attempt. */
 	if (progfd != -1)
 		bpf_prog_detach(cgfd, atype);
+	bpf_object__close(test->obj);
 	close(progfd);
 	printf("[%s]\n", err ? "FAIL" : "PASS");
 	return err;