Fix locale dependent behaviour in run-test.sh

'stat ... | grep Modify' fails on non english locales. stat -c '%y'
used in most of the places, but one exception remained.

test/run-test.sh

@@ -155,9 +155,9 @@ dotest "Keep mtime of the font directory"
 prep
 cp "$FONT1" "$FONTDIR"
 touch -d @0 "$FONTDIR"
-stat "$FONTDIR" | grep Modify > out1
+stat -c '%y' "$FONTDIR" > out1
 $FCCACHE "$FONTDIR"
-stat "$FONTDIR" | grep Modify > out2
+stat -c '%y' "$FONTDIR" > out2
 if cmp out1 out2 > /dev/null ; then : ; else
     echo "*** Test failed: $TEST"
     echo "mtime was modified"