caddy1: fix build (#97988)

main.go gets overwritten in order to build caddy with telemetry
disabled, but the global variable `run` got neglected, and this in turn
broke the test in caddy/main_test.go.

This commit fixes that, and build can now complete.

(cherry picked from commit c814b0e)

pkgs/servers/caddy/v1.nix

@@ -21,9 +21,10 @@ buildGoModule rec {
     cat << EOF > caddy/main.go
     package main
     import "github.com/caddyserver/caddy/caddy/caddymain"
+    var run = caddymain.Run // replaced for tests
     func main() {
       caddymain.EnableTelemetry = false
-      caddymain.Run()
+      run()
     }
     EOF
   '';