With a recent upgrade to an early access build for JDK 15,
ServerHttpsRequestIntegrationTests began failing since Netty's
SelfSignedCertificate could not be properly initialized.
This commit adds a test fixture dependency on BouncyCastle which is now
needed by Netty's SelfSignedCertificate on JDK 15 or higher, since JDK 15
no longer supports the javax.security.cert.X509Certificate.
See: https://bugs.openjdk.java.net/browse/JDK-8241039
5392ac2e07