Add tests for more row patterns with COPY FROM .. (ON_ERROR ignore)

Add tests for more row patterns with COPY FROM .. (ON_ERROR ignore)

While digging into the code of this feature, I got confused by the fact
that a line is skipped when a value cannot be converted to its expected
attribute even if the line has fewer attributes than the target
relation.  The tests had a check for the case of an empty line, this
commit a couple more patterns where a line is incomplete, but skipped
because of a conversion error.

Reviewed-by: Bharath Rupireddy
Discussion: https://postgr.es/m/Ze_7kZqexdt0BiyC@paquier.xyz