fix(output): normalize severity values to prevent HTML report failure #7875

Job	Run time
Documentation	3m 5s
Linux tests (3.9)	6m 17s
Long tests on Python 3.13 (language parsers)	5m 0s
Linux tests (3.10)	6m 42s
Long tests on Python 3.13	12m 15s
Linux tests (3.11)	6m 10s
Linux tests (3.12)	6m 23s
Long tests on Python 3.13 (scanners)	20m 46s
Long tests on Python 3.13 (synchronous)	6m 4s
Tests that may fail due to network or HTML	2m 58s
Windows long tests	1h 19m 59s
	2h 35m 39s

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