Rename primeCountApprox() to primeCountUpper() #61

Job	Run time
linux_clang (ubuntu-latest, Debug)	3m 41s
linux_gcc (ubuntu-latest, Debug)	5m 3s
linux_clang (ubuntu-latest, Release)	1m 38s
linux_gcc_valgrind	1m 18s
linux_gcc (ubuntu-latest, Release)	2m 9s
linux_gcc_sanitizers	2m 22s
macos_clang (macos-latest, Debug)	4m 19s
windows_mingw64 (windows-latest, Debug)	5m 34s
macos_clang (macos-latest, Release)	2m 14s
windows_msvc2022	1m 38s
windows_mingw64 (windows-latest, Release)	2m 55s
	32m 51s

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