[BUGIFX] Typo in code sample

The code sample in section "Complex data submission" of file
ApiOverview/Typo3CoreEngine/UsingTcemain/Index.rst contains
a call to a wrong method name.

Resolves: #59491
Releases: 6.2
Change-Id: Ib6923b52cae36807c73559ff32af23ec9cb9036c