Tests: correctly shutdown ssl for reproducible session reuse tests.

Previously, session reuse tests in stream_ssl_certificate.t were prone
to testing errors, since the client doesn't write any application data
before closing a connection, which is done so to pass tests on win32.
In this case, the server may happened to get an unexpected eof meaning
that it will abandon that session.  This is specific to stream testing
pattern, changes to ssl_certificate.t are applied too for consistency.
This is also specific to SSL_R_UNEXPECTED_EOF_WHILE_READING, which is
implemented in OpenSSL 3.0.0.

ssl_certificate.t

diff --git a/ssl_certificate.t b/ssl_certificate.t
index 80e7c88..c15ec2b 100644
--- a/ssl_certificate.t
+++ b/ssl_certificate.t
@@ -200,6 +200,7 @@
 	my ($s, $ssl) = get_ssl_socket($host, $port, $ctx) or return;
 	Net::SSLeay::write($ssl, 'GET / HTTP/1.0' . CRLF . CRLF);
 	my $r = Net::SSLeay::read($ssl);
+	Net::SSLeay::shutdown($ssl);
 	$s->close();
 	return $r unless wantarray();
 	return ($s, $ssl);

stream_ssl_certificate.t

diff --git a/stream_ssl_certificate.t b/stream_ssl_certificate.t
index 1655b65..56f6186 100644
--- a/stream_ssl_certificate.t
+++ b/stream_ssl_certificate.t
@@ -182,6 +182,7 @@
 	my ($host, $port, $ctx) = @_;
 	my ($s, $ssl) = get_ssl_socket($host, $port, $ctx) or return;
 	my $r = Net::SSLeay::read($ssl);
+	Net::SSLeay::shutdown($ssl);
 	$s->close();
 	return $r unless wantarray();
 	return ($s, $ssl);