build tarball using ustar format for better compatibility

Tell tar to use the ustar format when building the release tarball.
ustar is the baseline format that doesn't include extra headers that
will cause warnings on any other tar version. Without it, the archive
will often end up with headers like
`LIBARCHIVE.xattr.com.apple.quarantine`, which will produce warnings
when extracted with GNU tar.

Makefile.PL

@@ -29,5 +29,6 @@ WriteMakefile(
     },
   },
   PREREQ_PM => {Mojolicious => '9.0', 'YAML::XS' => '0.67'},
-  test      => {TESTS       => 't/*.t t/*/*.t'}
+  test      => {TESTS       => 't/*.t t/*/*.t'},
+  dist      => {TARFLAGS    => '-c -v --format=ustar -f' },
 );