test/run_tests.pl: Make sure to exit with a code that's understood universally

TAP::Parser::Aggregator::has_errors may return any number, not just 0
and 1.  With Perl on VMS, any number from 2 and on is interpreted as a
VMS status, the 3 lower bits are the encoded severity (1 = SUCCESS,
for example), so depending on what has_errors returns, a test failure
might be interpreted as a success.  Therefore, it's better to make
sure the exit code is 0 or 1, nothing else (they are special on VMS,
and mean SUCCESS or FAILURE, to match Unix conventions).

Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3880)