Fix calculation of number of bins in FindGroup #7526

Job	Run time
r-sanitizers (ubuntu-latest, R-devel, gcc ASAN/UBSAN)	20m 26s
r-sanitizers (ubuntu-latest, R-devel, clang ASAN/UBSAN)	33m 8s
r-package (ubuntu-latest, gcc, R 3.6, cmake)	9m 16s
r-package (debian, R-devel, clang)	19m 12s
r-package (ubuntu-latest, gcc, R 4.3, cmake)	16m 37s
r-package (ubuntu-latest, clang, R 3.6, cmake)	8m 52s
r-package (ubuntu-latest, clang, R 4.3, cmake)	13m 13s
r-package (macOS-latest, gcc, R 4.3, cmake)	12m 24s
r-package (macOS-latest, clang, R 4.3, cmake)	11m 6s
r-package (windows-latest, MINGW, R 3.6, cmake)	14m 52s
r-package (windows-latest, MINGW, R 4.3, cmake)	20m 35s
r-package (windows-2019, MSVC, R 3.6, cmake)	17m 42s
r-package (windows-2022, MSVC, R 4.3, cmake)	25m 12s
r-package (windows-latest, MINGW, R 3.6, cran)	27m 5s
r-package (windows-latest, MINGW, R 4.3, cran)	30m 19s
r-package (ubuntu-latest, gcc, R 4.3, cran)	20m 13s
r-package (macOS-latest, clang, R 4.3, cran)	20m 6s
r-rchk (ubuntu-latest, gcc, R 4.3, cran)	10m 10s
all-r-package-jobs-successful	3s
	5h 30m 31s

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