cmd/go: suppress SSH password prompts when fetching modules or repos

We were already setting GIT_SSH_COMMAND (if unset) to explicitly
include 'ControlMaster=no' in order to disable connection pooling.
Now we also set 'BatchMode=yes' to suppress password prompts for
password-protected keys.

While we're here, we also set GCM_INTERACTIVE=never to suppress
similar prompts from the Git Credential Manager for Windows.

Fixes #44904

Change-Id: Iebb050079ff7dd54d5b944c459ae212e9e6f2579
Reviewed-on: https://go-review.googlesource.com/c/go/+/300157


Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>