Fix warning with send_file.t on Windows:

File::Temp on Windows uses `FILE_FLAG_DELETE_ON_CLOSE` semantics.
The temp file is deleted when the OS file handle is closed. So
`close $temp` deletes the file, and `send_file($temp->filename, ...)`
subsequently fails the `$file_path->exists` check, which calls
`$err_response->(403)`, setting content type to `text/plain` and
returning a 403.

So instead, we replace the File::Temp usage in the
`check_content_type` route with
`Path::Tiny::path(__FILE__)->absolute->stringify`, which is the same
pattern the `/no_streaming` and `/options_streaming` routes already
use. The test only needs a readable file to verify that
`content_type => 'image/png'` overrides MIME auto-detection. It
doesn't require a temp file.

The core `send_file` implementation handles Windows absolute paths
correctly (via the fix in df6a0a4). The issue was purely with the
test's temp-file lifecycle assumption.

Author: xsawyerx

t/dsl/send_file.t

@@ -6,7 +6,6 @@ use Encode 'encode_utf8';
 use Test::More;
 use Plack::Test;
 use HTTP::Request::Common;
-use File::Temp;
 use Path::Tiny ();
 use Ref::Util qw<is_coderef>;
 
@@ -45,11 +44,8 @@ use Ref::Util qw<is_coderef>;
     };
 
     get '/check_content_type' => sub {
-        my $temp = File::Temp->new();
-        print $temp "hello";
-        close $temp;
-        send_file($temp->filename, content_type => 'image/png',
-                                   system_path  => 1);
+        my $file = Path::Tiny::path(__FILE__)->absolute->stringify;
+        send_file($file, content_type => 'image/png', system_path => 1);
     };
 
     get '/no_streaming' => sub {