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
@@ -1856,7 +1856,8 @@ guess_file_type(const string& file_path, bool look_through_compression)
       || 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;
 
   file_type r = FILE_TYPE_UNKNOWN;