Fix Goroutine Leak of Nomad execute command

that was triggered when [the execution timeout got exceeded, the runner got destroyed, or the WebSocket connection to CodeOcean closed] and the Allocation did not react to the SIGQUIT within the grace period.

internal/runner/nomad_runner.go

@@ -281,7 +281,10 @@ func (r *NomadJob) executeCommand(ctx context.Context, command string, privilege
 	stdin io.ReadWriter, stdout, stderr io.Writer, exit chan<- ExitInfo,
 ) {
 	exitCode, err := r.api.ExecuteCommand(r.id, ctx, command, true, privilegedExecution, stdin, stdout, stderr)
-	exit <- ExitInfo{uint8(exitCode), err}
+	select {
+	case exit <- ExitInfo{uint8(exitCode), err}:
+	case <-ctx.Done():
+	}
 }
 
 func (r *NomadJob) handleExitOrContextDone(ctx context.Context, cancelExecute context.CancelFunc,