selftests/harness: Prevent infinite loop due to Assert in FIXTURE_TEARDOWN

This patch addresses an issue in the selftests/harness where an
assertion within FIXTURE_TEARDOWN could trigger an infinite loop.
The problem arises because the teardown procedure is meant to
execute once, but the presence of failing assertions (ASSERT_EQ(0, 1))
leads to repeated attempts to execute teardown due to
the long jump mechanism used by the harness for handling assertions.

To resolve this, the patch ensures that the teardown process
runs only once, regardless of assertion outcomes, preventing
the infinite loop and allowing tests to fail.

A simple test demo(test.c):
 #include "kselftest_harness.h"

FIXTURE(f)
{
	int fd;
};

FIXTURE_SETUP(f)
{
	self->fd = 0;
}

FIXTURE_TEARDOWN(f)
{
	TH_LOG("TEARDOWN");
	ASSERT_EQ(0, 1);
	self->fd = -1;
}

TEST_F(f, open_close)
{
	ASSERT_NE(self->fd, 1);
}

TEST_HARNESS_MAIN

will always output the following output due to a dead loop until timeout:
 # test.c:15:open_close:TEARDOWN
 # test.c:16:open_close:Expected 0 (0) == 1 (1)
 # test.c:15:open_close:TEARDOWN
 # test.c:16:open_close:Expected 0 (0) == 1 (1)
 ...

But here's what we should and expect to get:
 TAP version 13
 1..1
 # Starting 1 tests from 2 test cases.
 #  RUN           f.open_close ...
 # test.c:15:open_close:TEARDOWN
 # test.c:16:open_close:Expected 0 (0) == 1 (1)
 # open_close: Test terminated by assertion
 #          FAIL  f.open_close
 not ok 1 f.open_close
 # FAILED: 0 / 1 tests passed.
 # Totals: pass:0 fail:1 xfail:0 xpass:0 skip:0 error:0

also this is related to the issue mentioned in this patch
https://patchwork.kernel.org/project/linux-kselftest/patch/e2ba3f8c-80e6-477d-9cea-1c9af820e0ed@alu.unizg.hr/

Signed-off-by: Shengyu Li <shengyu.li.evgeny@gmail.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>