patch 9.1.0958: filetype: supertux2 config files detected as lisp

patch 9.1.0958: filetype: supertux2 config files detected as lisp

Problem:  filetype: supertux2 config files detected as lisp
Solution: detect supertux2 config files as scheme instead
          (Wu, Zhenyu)

References:
https://github.com/SuperTux/supertux/wiki/S-Expression

supertux uses #t and #f as bool type, which is same as scheme, not
common lisp

closes: #16287

Signed-off-by: Wu, Zhenyu <wuzhenyu@ustc.edu>
Signed-off-by: Christian Brabandt <cb@256bit.org>