fix changelog typos

6 jobs for master in 12 minutes and 46 seconds
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passed #6753
fp-timing
build-coq.8.6.1

00:02:06

passed #6752
fp-timing
build-coq.8.7.1

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passed #6754
opam

00:00:16

 
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passed #6757
fp-timing
build-coq.8.6.0

00:05:06

passed #6756
fp-timing
build-coq.8.7.0

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passed #6755
fp-timing
build-coq.8.7.dev

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