Set http.version=HTTP/1.1 in supports_gvfs_protocol() (git-for-windows#759)

The way the `gvfs-helper` command operates is apparently incompatible
with HTTP/2, that's why microsoft#754 tried
to enforce HTTP/1.1 in Scalar clones accessing Azure Repos.

However, this fix was incomplete for the `scalar clone` part because it
made the HTTP/1.1 enforcement contingent on the test whether the remote
repository supports the GVFS protocol or not, and that test did _not_
enforce HTTP/1.1.

Let's fix that Catch-22 by enforcing HTTP/1.1 usage during that GVFS
Protocol capability test.

Author: dscho

scalar.c

@@ -467,7 +467,8 @@ static int supports_gvfs_protocol(const char *url, char **cache_server_url)
 		return 0;
 
 	cp.git_cmd = 1;
-	strvec_pushl(&cp.args, "gvfs-helper", "--remote", url, "config", NULL);
+	strvec_pushl(&cp.args, "-c", "http.version=HTTP/1.1",
+		     "gvfs-helper", "--remote", url, "config", NULL);
 	if (!pipe_command(&cp, NULL, 0, &out, 512, NULL, 0)) {
 		long l = 0;
 		struct json_iterator it =