Tests: skip "no headers" test in h2_proxy_cache.t on win32.

Small limit rate doesn't work on this platform which breaks test preconditions.
diff --git a/h2_proxy_cache.t b/h2_proxy_cache.t
index f8845b7..43f3169 100644
--- a/h2_proxy_cache.t
+++ b/h2_proxy_cache.t
@@ -157,6 +157,9 @@
 ok(!grep ({ $_->{type} eq "DATA" } @$frames),
 	'proxy cache HEAD buffering off - no body');
 
+SKIP: {
+skip 'win32', 1 if $^O eq 'MSWin32';
+
 # client cancels stream with a cacheable request that was sent to upstream
 # HEADERS should not be produced for the canceled stream
 
@@ -168,6 +171,8 @@
 $frames = $s->read(all => [{ sid => $sid, fin => 0x4 }], wait => 1.2);
 ok(!(grep { $_->{type} eq "HEADERS" } @$frames), 'no headers');
 
+}
+
 # client closes connection after sending a cacheable request producing alert
 
 $s = Test::Nginx::HTTP2->new();