Fixed invalid regex handling in filterwarnings #5987

Job	Run time
package	18s
build (windows-py39-unittestextras)	26m 7s
build (windows-py39-pluggy)	6m 35s
build (windows-py39-xdist)	6m 32s
build (windows-py310)	6m 41s
build (windows-py311)	16m 57s
build (windows-py312)	19m 18s
build (windows-py313)	16m 12s
build (ubuntu-py39-lsof-numpy-pexpect)	27m 35s
build (ubuntu-py39-pluggy)	5m 12s
build (ubuntu-py39-freeze)	47s
build (ubuntu-py39-xdist)	5m 23s
build (ubuntu-py310-xdist)	6m 22s
build (ubuntu-py311)	19m 17s
build (ubuntu-py312)	22m 14s
build (ubuntu-py313-pexpect)	22m 58s
build (ubuntu-pypy3-xdist)	7m 57s
build (macos-py39)	5m 48s
build (macos-py310)	4m 47s
build (macos-py312)	4m 11s
build (macos-py313)	4m 35s
build (doctesting)	45s
build (plugins)	48s
check	1s
	3h 57m 20s

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