Fix wrong direction of text Y axis offset.

[ismailsunni]

• OpenLayers: https://openlayers.org/en/latest/apidoc/module-ol_style_Text-Text.html
  • offsetY: Vertical text offset in pixels. A positive will shift the text down.
• MFP: https://mapfish.github.io/mapfish-print-doc/styles.html
  • labelYOffset (ECQL) - (Point Placement) the amount to offset the label along the y axis. negative number offset to the top of the printing

UPDATE:

It seems there might be a confusion in myself.

From the documentation itself, both description above seems the same. But when I try to print, there is an unexpected result

[ger-benjamin]

Not tested, but code is ok, and I trust you :-)