Fix partial cloning a repo (#18373) (#18377)

* Fix partial cloning a repo (#18373)

- Backport from: #18373
- Backport isn't 1-1, because the frontport had a refactor in that area,
which v1.16 doesn't have.

* Include diff & use copy

* Add partial clone test

* patch

* Apply suggestions from code review

* globalArgs first

* avoid copy but make GlobalCMDArgs append first

* please linter

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: 6543 <6543@obermui.de>

routers/web/repo/http.go

@@ -491,7 +491,10 @@ func serviceRPC(h serviceHandler, service string) {
 	defer finished()
 
 	var stderr bytes.Buffer
-	cmd := exec.CommandContext(ctx, git.GitExecutable, service, "--stateless-rpc", h.dir)
+	args := make([]string, len(git.GlobalCommandArgs))
+	copy(args, git.GlobalCommandArgs)
+	args = append(args, []string{service, "--stateless-rpc", h.dir}...)
+	cmd := exec.CommandContext(ctx, git.GitExecutable, args...)
 	cmd.Dir = h.dir
 	cmd.Env = append(os.Environ(), h.environ...)
 	cmd.Stdout = h.w