fix(ingest/bigquery): Filter out fine grained lineage with no upstreams

[asikowitz]

Test confirmed to fail before the 1 line change

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[asikowitz]

column_mapping[out_column] = frozenset(
                upstream_column_info.column
                for upstream_column_info in column_lineage.upstreams
                if upstream_column_info.table == table_urn
            )

This line is the true culprit. I could factor this out and only set column_mapping[out_column] if there are upstreams for it, but seemed easier to filter out later on