tests: correct extension of test_a_star expected result

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>

diff --git a/tests/sav/test_a_star.sav b/tests/sav/test_a_star.res
similarity index 100%
rename from tests/sav/test_a_star.sav
rename to tests/sav/test_a_star.res