add format specifier tp single-symbol notation

Works around Coq bug #7731
7 jobs for master in 14 minutes and 9 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #13723
fp
build-coq.8.6.0

00:03:01

passed #13722
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build-coq.8.6.1

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passed #13721
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build-coq.8.7.0

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passed #13720
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build-coq.8.7.1

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passed #13719
fp-timing
build-coq.8.7.2

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passed #13718
fp
build-coq.8.8.0

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passed #13717
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build-coq.dev

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