Detect .apk as tarballs.

This is based on https://github.com/void-linux/void-packages/blob/c4880df0bb88e6e9ba08bd22f2ada592a6e60fc7/srcpkgs/libabigail/patches/xbps.patch.

--- a/src/abg-tools-utils.cc
+++ b/src/abg-tools-utils.cc
@@ -690,7 +690,8 @@
       || string_ends_with(file_path, ".tlz")
       || string_ends_with(file_path, ".tar.Z")
       || string_ends_with(file_path, ".taz")
-      || string_ends_with(file_path, ".tz"))
+      || string_ends_with(file_path, ".tz")
+      || string_ends_with(file_path, ".apk"))
     return FILE_TYPE_TAR;
 
   ifstream in(file_path.c_str(), ifstream::binary);