fixes #1733 (`ln_eq0`) #254

Job	Run time
rocq-core	45s
coq	44s
mathcomp-analysis-single	14m 20s
mathcomp-classical	2m 50s
mathcomp-reals	2m 10s
mathcomp-analysis	12m 10s
mathcomp-experimental-reals	1m 41s
mathcomp-reals-stdlib	1m 25s
mathcomp-analysis-stdlib	1m 30s
	37m 35s

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