tests: fix checksums for png aspect ratio change

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

tests/ref/fate/vsynth1-mpng

@@ -1,4 +1,4 @@
-a8e7393fa534289eee9319ded7807f99 *tests/data/fate/vsynth1-mpng.avi
-12157242 tests/data/fate/vsynth1-mpng.avi
+be741137074c7d3b160e2eec464b8c61 *tests/data/fate/vsynth1-mpng.avi
+12158288 tests/data/fate/vsynth1-mpng.avi
 93695a27c24a61105076ca7b1f010bbd *tests/data/fate/vsynth1-mpng.out.rawvideo
 stddev:    3.42 PSNR: 37.44 MAXDIFF:   48 bytes:  7603200/  7603200

tests/ref/fate/vsynth2-mpng

@@ -1,4 +1,4 @@
-198a3d67c56e1b5b12bdd3ffa67d8128 *tests/data/fate/vsynth2-mpng.avi
-12557288 tests/data/fate/vsynth2-mpng.avi
+777cee2a95de980bc63861c9093ba908 *tests/data/fate/vsynth2-mpng.avi
+12558342 tests/data/fate/vsynth2-mpng.avi
 98d0e2854731472c5bf13d8638502d0a *tests/data/fate/vsynth2-mpng.out.rawvideo
 stddev:    1.26 PSNR: 46.10 MAXDIFF:   13 bytes:  7603200/  7603200