t/lib-httpd: pass through GIT_CONFIG_NOSYSTEM env

We set GIT_CONFIG_NOSYSTEM in our test scripts so that we do not accidentally read /etc/gitconfig and have it influence the outcome of the tests. But when running smart-http tests, Apache will clean the environment, including this variable, and the "server" side of our http operations will read it. You can see this breakage by doing something like: make ./git config --system http.getanyfile false make test which will cause t5561 to fail when it tests the fallback-to-dumb operation. We can fix this by instructing Apache to pass through the variable. Unlike with other variables (e.g., 89c57ab3's GIT_TRACE), we don't need to set a dummy value to prevent warnings from Apache. test-lib.sh already makes sure that GIT_CONFIG_NOSYSTEM is set and exported. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>