[BUGFIX] Updating identifiers does not work when := operator for value modification functions

[stigfaerch]

https://docs.typo3.org/p/oktopuce/site-generator/main/en-us/Administrators/UpdateTemplate/Index.html?highlight=mapinstring
This example in the documentation does not make much sense as the value modification functions needs the := operator, but updating currently only works with the equal operator.

      # Map all values in the string and exclude some of them
      # ext=SiteGenerator; table=tt_content; action=mapInString; ignoreUids=29,30
      multipleCeWithIgnore = addInList(28,29,30)

[stigfaerch]

@Oktopuce Also fixed in https://github.com/stigfaerch/site_generator/tree/issue_19

[Oktopuce]

Feature added with version 3.1.2.
Thanks Stig for the PR.