op/lex_assign.t: fix intermittent failures

op/lex_assign.t: fix intermittent failures

The bulk of this test script tests whether ops which are capable of
the OA_TARGLEX optimisation return the same results with lexical and
package var assignments, i.e.

    my $a;
    $a = OP;
    $b = OP;
    is($a,$b);

When OP is 'time', the two calls can return different times, resulting in
occasional intermittent failures. So move time into it's custom test which
can cope with a delta of 1.

Similarly if the op is <*>, parallel testing can result in temporary files
appearing in the current directory, resulting in different returns.
However, since glob doesn't actually have the 'T' (OA_TARGLEX) set in
regen/opcodes, this test is moot - so skip it.

If glob ever does ever get OA_TARGLEX, and so need to be tested, it may
require some subtlety, such as globbing for a pattern that won't match any
temporary files.