Fix more int conversions in FlatNotebook #173

Job	Run time
build-source-dist	8m 28s
Build wxPython documentation	45m 59s
build-wheels (ubuntu-22.04, 3.9, x64)	24m 15s
build-wheels (ubuntu-22.04, 3.10, x64)	23m 39s
build-wheels (ubuntu-22.04, 3.11, x64)	28m 46s
build-wheels (ubuntu-22.04, 3.12, x64)	24m 30s
build-wheels (ubuntu-22.04, 3.13, x64)	27m 49s
build-wheels (windows-2022, 3.9, x86)	23m 10s
build-wheels (windows-2022, 3.9, x64)	23m 4s
build-wheels (windows-2022, 3.10, x86)	24m 8s
build-wheels (windows-2022, 3.10, x64)	24m 17s
build-wheels (windows-2022, 3.11, x86)	25m 27s
build-wheels (windows-2022, 3.11, x64)	21m 53s
build-wheels (windows-2022, 3.12, x86)	23m 39s
build-wheels (windows-2022, 3.12, x64)	21m 57s
build-wheels (windows-2022, 3.13, x86)	25m 53s
build-wheels (windows-2022, 3.13, x64)	23m 7s
build-wheels (macos-13, 3.9, x64)	35m 8s
build-wheels (macos-13, 3.10, x64)	47m 23s
build-wheels (macos-13, 3.11, x64)	42m 50s
build-wheels (macos-13, 3.12, x64)	43m 3s
build-wheels (macos-13, 3.13, x64)	36m 44s
Upload wheels to snapshot-builds on wxpython.org	1m 22s
Publish Python distribution to PyPI	0s
Create GitHub Release and upload source	0s
	10h 26m 31s

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