[#33700] Fix for "duplicate key on insert detected" errors  in FinderIndexerHelper::addContentType

When indexing content via a finder plugin which may have multiple mime types (e.g. document management systems, pdf, doc, zip etc.), adding a new mime type will work, but if another document with the same mime type exists, consecutive getting the type id results in a duplicate insert in table #__finder_types.
This is due to that the static method variable $types is initialized on the first call of the method and does not take in account mime types inserted after initialization.

The fix adds the newly inserted mime type into $types hash, so that calling this method againg with the same mimetype results in a positive lookup within the hash.