Add astc files so they are checked in with LFS

Author: Erik-White

.gitattributes

@@ -126,6 +126,7 @@
 *.dds               filter=lfs diff=lfs merge=lfs -text
 *.ktx               filter=lfs diff=lfs merge=lfs -text
 *.ktx2              filter=lfs diff=lfs merge=lfs -text
+*.astc              filter=lfs diff=lfs merge=lfs -text
 *.pam               filter=lfs diff=lfs merge=lfs -text
 *.pbm               filter=lfs diff=lfs merge=lfs -text
 *.pgm               filter=lfs diff=lfs merge=lfs -text