Adds an advanced-usage section explaining the 'self signed certificate in
certificate chain' error seen on GitHub Enterprise Server and behind
TLS-inspecting proxies. Recommends the secure fix of trusting the internal
CA via NODE_EXTRA_CA_CERTS (or the OS trust store on self-hosted runners),
with a GitHub Enterprise callout, and warns against disabling TLS
verification since the JDK download has no checksum fallback.
Refs #640
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
a9a46fbe09