TestScripts/mod_get_svn would stop with the following prompt if the real
user didn't have vcs-test.golang.org in their known_hosts file:
The authenticity of host 'vcs-test.golang.org (35.184.38.56)' can't be established.
ECDSA key fingerprint is SHA256:[...]
Are you sure you want to continue connecting (yes/no/[fingerprint])?
This was bad because it relied on the user's real ssh known_hosts file.
Worse even, if the user didn't expert or notice the prompt, it could
hang a 'go test' run for quite a while.
Work around that by forcing svn to not use ssh at all. Other potentially
better approaches were tried, but none worked on svn 1.12.2 with openssh
8.0p1.