[BUGFIX] Wrong property name for match_method

In the importer code, property "match_method" is tested as
"mapping_method" instead.

Resolves: #56629
Releases: 2.3
Change-Id: I1301cd7d3cabcbdd3932508b572b3526a1083c1f
Reviewed-on: https://review.typo3.org/29743
Reviewed-by: Francois Suter
Tested-by: Francois Suter