config(qemu): disable file locking on BIOS

In QEMU, when file locking is enabled and supported, the image
file will be opened with O_RDWR even if readonly=on. Due to some
race condition during QEMU startup, sometimes it detects that
locks are supported and in those times, the BIOS read from a read
only bookmark will fail.

Fixes #5523

Configuration/UTMQemuConfiguration+Arguments.swift

@@ -385,8 +385,9 @@ import Virtualization // for getting network interfaces
                 "if=pflash"
                 "format=raw"
                 "unit=0"
-                "file="
+                "file.filename="
                 bios
+                "file.locking=off"
                 "readonly=on"
                 f()
                 f("-drive")