golang: Update to 1.19.6

go1.19.6 (released 2023-02-14) includes security fixes to the
crypto/tls, mime/multipart, net/http, and path/filepath packages,
as well as bug fixes to the go command, the linker, the runtime,
and the crypto/x509, net/http, and time packages.

Signed-off-by: Tianling Shen <cnsztl@immortalwrt.org>