cmd/go/internal/vcweb: set GIT_PROTOCOL in the git CGI handler
This works around a bug in 'git http-backend' that was fixed in
Git 2.34.0,¹ and will hopefully allow the tests in
cmd/go/internal/modfetch/codehost to pass reliably using older
Git releases (I tested with 2.30.2).
¹https://github.com/git/git/commit/
ff6a37c99e3343633c53f56789afcc8f8165d276
Fixes #56881.
Change-Id: Icd2e4d252d5f712685d146f34e11922dd0c41ff0
Reviewed-on: https://go-review.googlesource.com/c/go/+/549795
Reviewed-by: Michael Matloob <matloob@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>