veb: skip graceful_shutdown_test on tcc-linux, and bound shutdown timeout

The test hangs indefinitely on the tcc-linux CI job, pinning the
watchdog for the entire 6h timeout. Skip it under tinyc until the
underlying tcc/spawn interaction is understood, and pass an explicit
5s timeout to server.shutdown() so future regressions fail fast
instead of hanging CI.

Author: medvednikov

vlib/veb/tests/graceful_shutdown_test.v

@@ -1,4 +1,4 @@
-// vtest build: !windows // fasthttp.Server.run is not implemented on windows yet
+// vtest build: !windows && !tinyc // fasthttp.Server.run is not implemented on windows; the test hangs intermittently when built with tcc on linux CI
 import net
 import net.http
 import time
@@ -41,7 +41,7 @@ fn (app &GracefulShutdownApp) shutdown_now() {
 	if server == unsafe { nil } {
 		panic('veb server was not initialized')
 	}
-	server.shutdown() or { panic(err) }
+	server.shutdown(timeout: 5 * time.second) or { panic(err) }
 }
 
 fn run_graceful_shutdown_app(mut app GracefulShutdownApp, port int) {