The Scintilla API SCI_SETACCESSIBILITY is a no-op operation on windows, meaning it does nothing.
However, you can try to disable the Direct2D feature and force Scintilla to use the old drawing code and of course the default windows cursor.
To do that, open the TortoiseSVN settings dialog, go to "Advanced" and there search for the entry "ScintillaDirect2D" and set it to "false".
Maybe that helps.
Stefan