virt_firmware_check_phys_bits: update pattern for limitation_msg #6825

Job	Run time
Cfg lint	14s
Commit lint	18s
Python 3.6	1m 16s
Python 3.9	1m 39s
PR title	1s
Cartesian syntax (qemu/tests/cfg/virt_firmware_check_phys_bits.cfg)	7s
	3m 35s

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