Go 1.26's url.Parser is stricter and made our tests elsewhere fail
with this scheme because when these listen addresses get shoved
into a URL, it can't parse back out.
I verified this makes tests elsewhere pass with Go 1.26.
Updates #18682
Change-Id: I04dd3cee591aa85a9417a0bbae2b6f699d8302fa
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>